MacFormat 1994 November/macformat-018.iso/Utility Spectacular/Developer/p2c1.20-a5.appl Folder/p2c 1.20a5/doc/p2c.man.text

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NAME
        p2c - Pascal to C translator, version 1.20
SYNOPSIS
        p2c [ options ] [ file [ module ] ]

DESCRIPTION
P2c is a tool for translating Pascal programs into C. The input consists of a set of source files in
any of the following Pascal dialects: HP Pascal, Turbo/UCSD Pascal, DEC VAX Pascal,
Oregon Software Pascal/2, Macintosh Programmer's Workshop Pascal, Sun/Berkeley Pascal.
Modula-2 syntax is also supported. Output is a set of .c and .h files that comprise an equivalent
program in any of several dialects of C. Output code may be kept machine- and dialect-
independent, or it may be targeted to a specific machine and compiler. Most reasonable Pascal
programs are converted into fully functional C which will compile and run with no further
modifications, although p2c sometimes chooses to generate readable code at the expense of
absolute generality.

P2c endeavors to insert notes and warning messages into the output code to point out areas
which may require human intervention. Output code is arranged to be readable and efficient, and
to make use of C idioms wherever possible. The main goal of the translation is to produce C
files which are pleasant and "natural" enough to be acceptable as the new source files for a
program. In a pinch, p2c will also serve as an ad hoc Pascal compiler.

Code generated by p2c normally does not assume characters are signed or unsigned. Also, it
assumes int is the same as either short or long but does not depend on which. However, if int is
not the same as long it is best to use a modern C compiler which supports prototypes. Generated
code does not require an ANSI-compatible compiler (unless ANSI-style code is requested), but
it does use various ANSI-standard library routines.

All generated code includes the file <p2c.h> which in turn includes <stdio.h> and various other
common resources. Also, many translated programs will need to be linked with the run-time
library, typically -lp2c.

Given a file name, p2c reads from the specified file and outputs to a file with a .c suffix added or
substituted. For example,
    p2c myfile.p

reads from myfile.p to produce the file myfile.c. The input file may contain a Pascal main
program or a single Pascal module (or "unit" in UCSD Pascal nomenclature), or it may just
contain a number of procedures and declarations. P2c is designed to work for correct input
programs. That is, it will accept partial programs but may occasionally crash if the input refers to
undefined symbols.

If the input is a module, the translator will also produce a file module .h containing a translation
of the module's interface section. The implementation section may be omitted in which case only
the .h file will be interesting. If the program or module has include files, these may cause
additional .c files to be generated depending on the value of the ExpandIncludes option (see
below).

If no file name is given, p2c reads Pascal from the standard input and writes the resulting C to
standard output (though a .h file may still be produced). If a file name and module name are
given, the file may include several modules (or units). The specified module is translated; any
others are skipped. The output files will be named module .c and module .h . P2c never
translates more than one module per run.

The input program or module may make use other modules. These modules may be referred to
explicitely.  P2c holds a search list of places to find modules which are imported, the ImportDir
search list. Modules for inlusion may as well reside in additional default input files which are
imported before beginning the translation.

When starting, p2c a number of configuration parameters are set. The default parameters are
stored in p2c’s resource fork as resource of type 'p2c  '. These default parameters can be modi
fied using ResEdit. Next the file "p2c preferences" is read for a number of configuration para
meters from the preferences folder. (The actual path used on your system may vary. The -i
option is a handy way to examine this file.) If the P2CRC environment variable is set, it gives
the name of a file to read instead of the system file; this file can start with Include
%H/"p2c preferences" to include the system file. Next, p2c attempts to read the file
“p2c preferences” in your input directory for further configuration.

OPTIONS

-o cfile    Use cfile in place of file .c or module .c as the primary output file. A single dash
('–o –') says to write the C code to the standard output.

-h hfile    Use hfile in place of module .h as the output file for interface text. This only has
effect if the input is an HP Pascal module or a Pascal unit.

-s sfile     Read interface text from sfile before beginning the translation. This file typically
contains one or more modules, often with implementation sections omitted for
speed, which the program or module being translated will use. (Typically the
ImportFrom and ImportDir parameters in p2crc are set up to allow p2c to locate
interface text without needing any -s options.) If there are several -s options in the
command, the sfiles are read from left to right.

-p n    Display progress of translation in the form of a line number/file name display. This
is refreshed every n lines, 25 by default.

-c prefsfile    Read local configuration commands from prefsfile instead of "p2c preferences".  A
dash ('–c –') in place of prefsfile causes no local configuration file to be used.

 -v    ("Vanilla.") Do not read from the system configuration file "p2c preferences". Since
some of the parameters in this file are required, the p2c resource must include those
parameters instead. This also suppresses the file named by the P2CRC environment
variable.

-H homedir    Use homedir as the p2c home directory. The system "p2c preferences" file will be
searched for in this directory.

-I pattern    Add pattern to the ImportDir search list of places to find modules which are
imported. The pattern should include a %s to represent the module name, and
should evaluate to a potential file name for that module's source code. For example,
::%s.p looks for <modulename>.p in the parent of the current directory.

 -i    This special option copies the p2c system configuration to the standard output in its
entirety. (It may be used with -H , but -i is most useful precisely when you don't
know the location of the home directory.)

 -q    Quiet mode. Suppresses output of status messages during translation.

-E n    Abort translation after n errors. If n is omitted it defaults to zero, which means
unlimited errors are allowed. Use -E 1 to make p2c halt after the first error.

 -e    Echo the Pascal source into the output file, surrounded by #ifdefs. This is the same
as the CopySource parameter in the "p2c preferences" file.

 -a    Produce modern ANSI C. This is a convenient override for the AnsiC parameter in
the "p2c preferences" file.

-L language    Select input language name, such as MPW, VAX or TURBO. This is a convenient
override for the Language parameter.

 -V    Verbose mode. This causes p2c to generate an additional ".log" file with further
details of the translation, such as a list of warnings and notes including those which
are suppressed in the regular output.

 -M0    Disable memory conservation. This prevents p2c from freeing various data
structures after translating each function, in case this new conservation feature
causes unforseen problems.

 -R    Regression testing mode. Formats notes and warning messages in a way that makes
it easier to run compare on the output of p2c.

P2c also understands a few debugging options which may occasionally be useful when tracking
down translation problems. The -d n option sets the "debug level" to n, a small integer which is
normally zero. Debugging output is written into the regular output file along with the C code; the
higher your n, the more "wallpaper" you get. Also, -t prints debugging information at every
Pascal token, -B n enables line-breaker debugging, and -C n enables comment placement
debugging.

CHOICE OF SOURCE LANGUAGE
The Language configuration parameter or -L command-line option tells p2c which Pascal dialect
to expect in the input file. Any language features which do not overlap between dialects are
supported all of the time. The Language parameter is consulted when a syntax or usage is
detected that has different meanings in two different dialects, and also to determine default
values for various other translation parameters as described below.

The following language words are supported by p2c. Names are case-insensitive.
 HP    HP Pascal. All features of HP Standard Pascal, the Pascal Workstation version, are
supported except as noted in BUGS below. Some features of MODCAL, HP's
extended Pascal, are also supported. This is a superset of ISO standard Pascal,
including conformant arrays and procedural parameters.

 HP-UX     HP Pascal, HP-UX version. Almost identical to the "HP" dialect.

 Turbo     Turbo Pascal 5.0 for the IBM PC. Few conflicts with HP Pascal, so the Language
parameter is not often needed for Turbo. (Most important is that the Turbo and HP
dialects use 16 and 32 bit integers, respectively.)

 UCSD     UCSD Pascal. Similar to Turbo in many ways.

 MPW     Macintosh Programmer's Workshop Pascal 2.0. This is the default language.
Should also do a pretty good job for Think Pascal. Object Pascal features are not
supported, nor is the fact that char variables are sometimes stored in 16 bits.

 VAX     VAX/VMS Pascal version 3.5. Most but not all language features supported. This
has not yet been tested on large programs.

 Oregon     Oregon Software Pascal/2. All features implemented.

 Berk     Berkeley Pascal with Sun extensions.

 Modula     Modula-2. Based on Wirth's Programming in Modula-2, 3rd edition. Proper setting
of the Language parameter is not optional. Translation will be incomplete in most
cases, but should be good enough to work with. Structure of local sub-modules is
essentially ignored; like-named identifiers may be confused. Type WORD is
translated as an integer, but type ADDRESS is translated as char * or void *; this
may cause inconsistencies in the output code.

    Modula-2 modules have two parts in separate files. Suppose these are called
foo.def (definition part) and foo.mod (implementation part) for module foo. Then a
pattern like %s.def must be included in the ImportDir list, and LibraryFile must be
changed to refer to system.m2 instead of system.imp. To translate the definition
part, give the command
         p2c foo.def
    to translate the definition part into files foo.h and foo.c ; the latter will usually be
empty. The command
        p2c -s foo.def foo.mod
    will translate the implementation part into file foo.c.

Even if all language features are supported for a dialect, some predefined functions may be
omitted. In these cases, the function call will be translated literally into C with a warning. Some
hand modification may be required.

CONFIGURATION PARAMETERS
P2c is highly configurable. The defaults are suitable for most applications, but customizing these
parameters will help you get the best possible translation. Since the output of p2c is intended to
be used as human-maintainable source code, there are many parameters for describing the
coding style and conventions you prefer. Others give hints about your program that help p2c to
generate more correct, efficient, or readable code.

The p2crc files contain a list of parameters, one per line. The system configuration file, which
may be viewed using the -i option to p2c, serves as an example of the proper format. Parameter
names are case-insensitive. If a parameter name occurs exactly once in the system p2crc, this
indicates that it must have a unique value and the last value given to it by the configuration files
is used. Other parameters are written several times in a row; these are lists to which each
configuration line adds an entry.

Many p2crc options take a numeric value of 0 or 1, roughly corresponding to "no" or "yes."
Sometimes a blank value or the value "def" corresponds to an intermediate "maybe" state. For
example, the stylistic option ExtraParens switches between copious or minimal parentheses in
expressions, with the default being a nice compromise intended to be best for readers with an
average knowledge of C operator precedences.

Configuration options may also be embedded in the source file in the form of Pascal comments:

    {ShortOpt=0} {AvoidName=fred}
    {FuncMacro slope(x,y)=atan2(y,x)*RadDeg}

disables automatic short-circuiting of and and or expressions, adds "fred" to the list of names to
avoid using in generated C code, and defines a special translation for the Pascal program's slope
function using the standard C atan2 function and a constant RadDeg presumably defined in the
program. Whitespace is generally not allowed in embedded parameters. The `=' sign is required
for embedded parameters, though it is optional in p2crc files. Comments within embedded
parameters are delimited by `##'. Numeric parameters may replace `=' with `+' or `-' to increase
or decrease the parameter; list-based parameters may use `-' to remove a name from a list rather
than adding it. Also, the parameter name by itself in comment braces means to restore the
parameter's value that was current before the last change:

    {VarFiles=0 ## Pass FILE *'s params by value even if VAR}    some declarations
    {VarFiles  ## Back to original FILE * passing}

causes the parameter VarFiles to have the value 0 for those few declarations, without affecting
the parameter's value elsewhere in the file.

If an embedded parameter appears in an include file or in interface text for a module, the effect of
the assignment normally carries over to any programs that included that file. If the parameter
name is preceded by a `*', then the assignment is automatically undone after the source file that
contains it ends:

    {IncludeFrom strings=<p2c/strings.h>}
    {*ExportSymbol=pascal_%s}
    module strings;

will record the location of the strings module's include file for the rest of the translation, but the
assignment of ExportSymbol pertains only to the module itself.

For the complete list of p2crc parameters, run p2c with the -i option. Here are some additional
comments on selected parameters:

ImportAll
Because Turbo Pascal only allows one unit per source file, p2c normally stops reading past
the word implementation in a file being scanned for interface text. But HP Pascal allows
several modules per file and so this would not be safe to do. The ImportAll option lets you
override the default behavior for your Pascal dialect.

AnsiC
This parameter selects which dialect of C to use. If 1, all conventions of ANSI C such as
prototypes, void * pointers, etc. are used. If 0, only strict K&R (first edition) C is used. The
default is to use "traditional UNIX C," which includes enum and void but not void * or
prototypes. Once again there are a number of other parameters which may be used to control
the individual features if just setting AnsiC is not enough.

C++
At present p2c does not use much of C++ at all. The default action is to generate code that
will compile in either language.

UseVExtern
Many non-UNIX linkers prohibit variables from being defined (not declared) by more than
one source file. One module must declare, e.g., "int foo;", and all others must declare
"extern int foo;". P2c accomplishes this by declaring public variables "vextern" in header
files, and arranging for the macro vextern to expand to extern or to nothing when
appropriate. If you set UseVExtern =0 p2c will instead declare variables in a simpler way
that works only on UNIX-style linkers.

UseAnyptrMacros
Certain C reserved words have meanings which may vary from one C implementation to
another. P2c uses special capitalized names for these words; these names are defined as
macros in the file p2c.h which all translated programs include. You can set
UseAnyptrMacros = 0 to disable the use of these macros. Note that the functions of many
of these macros can also be had directly using other parameters; for example, UseConsts
allows you to specify whether your target language recognizes the word const in constant
declarations. The default is to use the Const macro instead, so that your code will be portable
to either kind of implementation.

Signed expands to the reserved word signed if that word is available, otherwise it is given a
null definition. Similarly, Const expands to const if that feature is available. The words
Volatile and Register are also defined in p2c.h, although p2c does not use them at present.
The word Char expands to char by default, but might need to be redefined to signed char or
unsigned char in a particular implementation. This is used for the Pascal character type;
lowercase char is used when the desired meaning is "byte," not "character."

The word Static always expands to static by default. This is used in situations where a
function or variable is declared static to make it local to the source file; lowercase static is
used for static local variables. Thus you can redefine Static to be null if you want to force
private names to be public for purposes of debugging.

The word Void expands to void in all cases; it is used when declaring a function with no
return value. The word Anyptr is a typedef for void * or char * as necessary; it represents a
generic pointer.

UsePPMacros

The p2c.h header also declares two macros for function prototyping, PP (x) and PV ().
These macros are used as follows:

        Void foo PP( (int x, int y, Char *z) );
        Char *bar PV( );

If prototypes are available, these macros will expand to

        Void foo (int x, int y, Char *z);
        Char *bar (void);

but if only old-style declarations are supported, you instead get

        Void foo ();
        Char *bar ();

By default, p2c uses these macros for all function declarations, but function definitions are
written in old-style C. The UsePPMacros parameter can be set to 0 to disable all use of PP
and PV , or it can be set to 1 to use the macros even when defining a function. (This is
accomplished by preceding each old-style definition with a PP -style declaration.) If you
know your code will always be compiled on systems that support prototyping, it is prettier
to set Prototypes =1 or simply AnsiC =1 to get true function prototypes.

EatNotes

Notes and warning messages containing any of these strings as sub-strings are not omitted.
Each type of message includes an identifier like [145] ; you can add this identifier to the
EatNotes list to suppress that message. Another useful form is to use a variable name or
other identifier to suppress warnings about that variable. The strings are a space-separated
list, and thus may not contain embedded spaces. To suppress notes around a section of
code, use, e.g., {EatNotes+[145]} and {EatNotes-[145]}. Most notes are generated during
parsing, but to suppress those generated during output the string may need to remain in the
list far beyond the point where it appears to be generated. Use the string "1" or "0" to disable
or enable all notes, respectively.

ExpandIncludes
The default action is to expand Pascal include files in-line. This may not be desirable if
include files are being used to simulate modules. With ExpandIncludes =0, p2c attempts to
convert include files containing only whole procedures and global declarations into
analogous C include files. This may not always work, though; if you get error messages,
don't use this option. By combining this option with StaticFunctions =0, then doing some
fairly minor editing on the result, you can convert a pseudo-modular Pascal program into a
truly modular collection of C source files.

ElimDeadCode
Some transformations that p2c does on the program may result in unreachable or "dead"
code. By default p2c removes such code, but sometimes it removes more than it should. If
you have "if false" segments which you wish to retain in C, you may have to set
ElimDeadCode =0.

SkipIndices
Normally Pascal arrays not based at zero are "shifted" down for C, preserving the total size
of the array. A Pascal array a[2..10] is translated to a C array a[9] with references like "a[i]"
changed to "a[i-2]" everywhere. If SkipIndices is set to a value of 2 or higher, this array
would instead be translated to a[11] with the first two elements never used. This
arrangement may generate incorrect code, though, for tricky source programs.

FoldConstants
Pascal non-structured constants generally translate to #define 's in C. Set this to 1 to have
constants instantiated directly into the code. This may be turned on or off around specific
constant declarations. Set this to 0 to force p2c to make absolutely no assumptions about the
constant's value in generated code, so that you can change the constant later in the C code
without invalidating the translation. The default is to allow p2c to take advantage of its
knowledge of a constant's value, such as by generating code that assumes the constant is
positive.

CharConsts
This governs whether single-character string literals in Pascal const declarations should be
interpreted as characters or strings. In other words, const a='x'; will translate to #define a
'x' if CharConsts =1 (the default), or to #define a "x" if CharConsts =0. Note that if p2c
guesses wrong, the generated code will not be wrong, just uglier. For example, if a is
written as a character constant but it turns out to be used as a string, p2c will have to write
char-to-string conversion code each time the constant is used.

VarStrings
In HP Pascal, a parameter of the form "var s : string" will match a string variable of any size;
a hidden size parameter is passed which may be accessed by the Pascal strmax function. You
can prevent p2c from creating a hidden size parameter by setting VarString =0. (Note that
each function uses the value of VarStrings as of the first declaration of the function that is
parsed, which is often in the interface section of a module.)

Prototypes
Control whether ANSI C function prototypes are used. Default is according to AnsiC . This
also controls whether to include parameter names or just their types in situations where
names are optional. The FullPrototyping parameter allows prototypes to be generated for
declarations but not for definitions (older versions of Lightspeed C required this). If you use
a mixture of prototypes and old-style definitions, types like short and float will be promoted
to int and double as required by the ANSI standard, unless PromoteArgs is used to override
this. The CastArgs parameter controls whether type-casts are used in function arguments;
by default they are used only if prototypes are not available.

StaticLinks
HP Pascal and Turbo Pascal each include the concept of procedure or function pointers,
though with somewhat different syntaxes. P2c recognizes both notational styles. Another
difference is that HP's procedure pointers can point to nested procedures, while Turbo's can
point only to global procedures. In HP Pascal a procedure pointer must be stored as a struct
containing both a pure C function pointer and a "static link," a pointer to the parent
procedure's locals. (The static link is NULL for global procedures.) This notation can be
forced by setting StaticLinks =1. In Turbo, the default ( StaticLinks =0) is to use plain C
function pointers with no static links. A third option ( StaticLinks =2) uses structures with
static links, but assumes the links are always NULL when calling through a pointer (if you
need compatibility with the HP format but know your procedures are global).

SmallSetConst
Pascal sets are translated into one of two formats, depending on the size of the set. If all
elements have ordinal values in the range 0..31, the set is translated as a single integer
variable using bit operations. (The SetBits parameter may be used to change the upper limit
of 31.) The SmallSetConst parameter controls whether these small-sets are used, and, if so,
how constant sets should be represented in C. For larger sets, an array of long is used. The
s [0] element contains the number of succeeding array elements which are in use. Set
elements in the range 0..31 are stored in the s [1] array element, and so on. Sets are
normalized so that s [ s [0]] is nonzero for any nonempty set. The standard run-time library
includes all the necessary procedures for operating on sets.

ReturnValueName
This is one of many "naming conventions" parameters. Most of these take the form of a
printf -like string containing a %s where the relevant information should go. In the case of
ReturnValueName , the %s refers to a function name and the resulting string gives the name
of the variable to use to hold the function's return value. Such a variable will be made if a
function contains assignments to its return value buried within the body, so that return
statements cannot conveniently be used. Some parameters ( ReturnValueName included) do
not require the %s to be present in the format string; for example, the standard p2crc file
stores every function's return value in a variable called Result.

AlternateName
P2c normally translates Pascal names into C names verbatim, but occasionally this is not
possible. A Pascal name may be a C reserved word or traditional C name like putc, or there
may be several like-named things that are hidden from each other by Pascal's scoping rules
but must be global in C. In these situations p2c uses the parameter AlternateName1 to
generate an alternative name for the symbol. The default is to add an underscore to the name.
There is also an AlternateName2 parameter for a second alternate name, and an
AlternateNamen parameter for the n th alternate name. (The value for this parameter should
include both a %s and a %d, in either order.) If these latter parameters are not defined, p2c
applies AlternateName1 many times over.

ExportSymbol
Symbols in the interface section for a Pascal module are formatted according to the value of
ExportSymbol , if any. It is not uncommon to use modulename_%s for this symbol; the
default is %s, i.e., no special treatment for exported symbols. If you also define the
Export_Symbol parameter, that format is used instead for exported symbols which contain
an underscore character. If %S (with a capital "S") appears in the format string it stands for
the current module name.

Alias
If the value of this parameter contains a %s, it is a format string applied to the names of
external functions or variables. If the value does not contain a %s, it becomes the name of
the next external symbol which is declared (after which the parameter is cleared).

Synonym
This creates a synonym for another Pascal symbol or keyword. The format is

    Synonym old-name = new-name

All occurrences of old-name in the input text are treated as if they were new-name by the
parser. If new-name is a keyword, old-name will be an equivalent keyword. If new-name is
the name of a predefined function, old-name will behave in the same way as that function,
and so on. If new-name is omitted, then occurrences of old-name are entirely ignored in the
input file. Synonyms allow you to skip over a keyword in your dialect of Pascal that is not
understood by p2c, or to simulate a keyword or predefined identifier of your dialect with a
similar one that p2c recognizes. Note that all predefined functions are available at all times; if
you have a library routine that behaves like, e.g., Turbo Pascal's getmem procedure, you
can make your routine a synonym for getmem even if you are not translating in Turbo mode.

NameOf
This defines the name to use in C for a specific symbol. It must appear before the symbol is
declared in the Pascal code; it is usually placed in the local p2crc file for the project. The
format is

    NameOf pascal-name = C-name

By default, Pascal names map directly onto C names with no change (except for the various
kinds of formatting outlined above). If the pascal-name is of the form module.name or
procedure.name then the command applies only to the instance of the Pascal name that is
global to that module, or local to that procedure. Otherwise, it applies to all usages of the
name.

VarMacro
This is analogous to NameOf , but specifically for use with Pascal variables. The righthand
side can be most any C expression; all references to the variable are expanded into that C
expression. Names used in the C expression are taken verbatim. There is also a
ConstMacro parameter for translating constants as arbitrary expressions. Note that the
variable on the lefthand side must actually be declared in the program or in a module that it
uses. The declaration for the variable will be omitted from the generated code unless the
Pascal-name appears in the expression: If you ask to replace i with i+1, the variable i will
still be declared but its value will be shifted accordingly. Note that if i appears on the
lefthand side of an assignment, p2c will use algebra to "solve" for i.

In all cases where p2c parses C expressions, all C operators are recognized except
compound assignments like `+='. (Increment and decrement operators are allowed.) All
variable and function names are assumed to have integer type, even if they are names that
occur in the actual program. A type-specification operator `::' has been introduced; it has the
same precedence as `.' or `->' but the righthand side must be a Pascal type identifier (built-in
or defined by your program previously to when the macro definition was parsed), or an
arbitrary Pascal type expression in parentheses. The lefthand argument is then considered to
have the specified type. This may be necessary if your macro is used in situations where the
exact type of the expression must be known (say, as the argument to a writeln ).

FieldMacro
Here the lefthand side must have the form record.field, where record is the Pascal type or
variable name for a record, and field is a field in that record. The righthand side must be a C
expression generally including the name record. All instances of that name are replaced by
the actual record being "dotted." For example,

    FieldMacro Rect.topLeft = topLeft(Rect)

translates a[i].topLeft into topLeft(a[i]), where a is an array of Rect.

FuncMacro
The lefthand side must be any Pascal function or procedure name plus a parameter list. The
number of parameters must match the number in the function's uses and declaration. Calls to
the function are replaced by the C expression on the righthand side. For example,

    FuncMacro PtInRect(p,r) = PtInRect(p,&r)

causes the second argument of PtInRect to be passed by reference, even though the
declaration says it's not. If the function in question is actually defined in the program or
module being translated, the FuncMacro will not affect the definition but it will affect all
calls to the function elsewhere in the module. FuncMacros can also be applied to predefined
or never-defined functions.

IncludeFrom
This specifies that a given module's header should be included from a given place. The
second argument may be surrounded by " " or < > as necessary; if the second argument is
omitted, no include directive will be generated for the module.

ImportFrom
This specifies that a given module's Pascal interface text can be found in the given file. The
named file should be either the source file for the module, or a specially prepared file with
the implementation section removed for speed. If no ImportFrom entry is found for a
module, the path defined by the ImportDir list is searched. Each entry in the path may
contain a %s, which expands to the name of the module. The default path looks for %s.pas
and %s.text in the current directory, then for --HOMEDIR--/%s.imp. (where --HOMEDIR--
is the p2c home directory.)

StructFunction
This parameter is a list of functions which follow the p2c semantics for structure-valued
functions (functions returning arrays, sets, and strings, and structs in primitive C dialects).
For these functions, a pointer to a return-value area is passed to the function as a special first
parameter. The function stores the result in this area, then returns a copy of the pointer. (The
standard C function strcpy is an example of this concept. Sprintf also behaves this way in
some dialects; it always appears on the StructFunction list regardless of the type of
implementation.) The system configuration file includes a list of common structured
functions so that p2c 's optimizer will know how to manipulate them.

StrlapFunction
Functions on this list are structured functions as above, but with the ability to work in-place;
that is, the same pointer may be passed as both the return value area and a regular parameter.

Deterministic Functions on this list have no side effects or side dependencies. An example is
the sin function in the standard math library; two calls with the same parameter values
produce the same result, and have no effects other than returning a value. P2c can make use
of this knowledge when optimizing code for efficiency or readability. Functions on this list
are also assumed to be relatively fast, so that it is acceptable to duplicate a call to the
function.

LeaveAlone Functions on this list are not subjected to the normal built-in translation rules
that p2c would otherwise use. For example, adding writeln to this list would translate
writeln statements blindly into calls to a C writeln() function, rather than being translated into
equivalent printf calls. The built-in translation is also suppressed if the function has a
FuncMacro .

BufferedFile
P2c normally assumes binary files will use read/write, not get/put/^ notation. A file buffer
variable will only be created for a file if buffer notation is used for it. For global file
variables this may be detected too late (a declaration without buffers may already have been
written). Such files can be listed in BufferedFile to force p2c to allocate buffers for them; do
this if you get a warning message that says it is necessary. Set BufferedFile =1 to buffer all
files, in which case UnBufferedFile allows you to force certain files not to have buffers.

StructFiles
If p2c still can't translate your file operations correctly, you can set StructFiles =1 to cause
Pascal files to translate into structs which include the usual C FILE pointer, as well as file
buffer and file name fields. While the resulting code doesn't look as much like native C, the
file structs will allow p2c to do a correct translation in many more cases.

CheckFileEOF
Normally only file-open operations are checked for errors. Additional error checking, such
as read-past-end-of-file, can be enabled with parameters like CheckFileEOF . These checks
can make the code very ugly! If I/O checking is enabled by the program ( "$iocheck on$" in
HP Pascal; {$I+} in Turbo; this is always the default state), these checks will generate fatal
errors unless enclosed in an HP Pascal try - recover construct. If I/O checking is disabled,
these will cause the global variable P_ioresult to be set zero or nonzero according to the
outcome. The default for most of these options is to check only when I/O checking is
disabled.


ISSUES

Integer size.
P2c normally generates code to work with either 16 or 32 bit ints. If you know your C integers
will be 16 or 32 bits, set IntSize appropriately. In particular setting IntSize =32 will generate
much cleaner code: p2c no longer must carefully cast function arguments between int and long.
These casts also will be unnecessary if ANSI prototypes are available. To disable int/long
casting because you know at least one of these cases will hold, set CastLongArgs =0. (The
CastArgs parameter similarly controls other types of casts, such as between ints and doubles.)
The Integer16 parameter controls whether Pascal integers are interpreted as 16 or 32 bits, or
translated as native C integers. The default value depends on the Language selected.

Signed/unsigned chars.
Pascal characters are normally "weakly" interpreted as unsigned; this is controlled by
UnsignedChar . The default is "either," so that C's native char type may be used even if its
signed-ness is unknown. Code that uses characters outside of the range 0-127 may need a
different setting. Alternatively, you can use the types {SIGNED} char and {UNSIGNED} char
in the few cases where it really matters. These comments are controlled by the SignedComment
and UnsignedComment parameters. (The type {UNSIGNED} integer is also recognized.) The
SignedChar parameter tells whether C characters are signed or unsigned (default is
"unknown"). The HasSignedChar parameter tells whether the phrase "signed char" is legal in
the output. If it is not, p2c may have to translate Pascal signed bytes into C shorts.

Special types.
P2c understands the following predefined Pascal type names:
    integer    signed integers depending on Integer16 ;
    longint    signed 32-bit integers;
    unsigned    unsigned 32-bit integers;
    sword    signed 16-bit integers;
    word    unsigned 16-bit integers;
    c_int    signed native C integers;
    c_uint    unsigned native C integers;
    sbyte    signed 8-bit integers;
    byte    unsigned 8-bit integers;
    real    floating-point numbers depending on DoubleReals ;
    single    single-precision floats;
    longreal ,
    double ,
and    extended    double-precision floats;
    pointer
and    anyptr    generic pointers (assignment-compatible with any pointer type);
    string    generic string of length StringDefault (normally 255);
also, the usual Pascal types
    char
    boolean,
and
    text .
(If your Pascal uses different names for these concepts, the Synonym option will come in
handy.)

Embedded code.
It is possible to write a Pascal comment containing C code to be embedded into the output. See
the descriptions of EmbedComment and its relatives in the system p2crc file. These techniques
are helpful if you plan to do repeated translations of code that is still being maintained in Pascal.

Comments and blank lines.
P2c collects the comments in a procedure into a list. All comments and statements are stamped
with serial numbers which are used to reattach comments to statements even after code has been
added, removed, or rearranged during translation. "Orphan" comments attached to statements
that have been lost are attached to nearby statements or emitted at the end of the procedure.
Blank lines are treated as a kind of comment, so p2c will also reproduce your usage of blank
lines. If the comment mechanism goes awry, you can disable comments with EatComments or
disable their being attached to code with SpitComments .

Indentation.
P2c has a number of parameters to govern indentation of code. The default values produce the
GNU Emacs standard indentation style, although p2c can do a better job since it knows more
about the code it is indenting. Indentation works by applying "indentation deltas," which are
either absolute numbers (which override the previous indentation), or signed relative numbers
(which augment the previous indentation). A delta of "+0" specifies no change in indentation.
All of the indentation options are described in the standard p2crc file.

Line breaking.
P2c uses an algorithm similar to the TeX typesetter's paragraph formatter for breaking long
statements into multiple lines. A "penalty" is assigned to various undesirable aspects of all
possible line breaks; the "badness" of a set of line breaks is approximately the sum of all the
penalties. Chief among these are serious penalties for overrunning the desired maximum line
length (default 78 columns), an infinite penalty for overrunning the absolute maximum line
length (default 90), and progressively greater penalties for breaking at operators deeply nested in
expressions. Parameters such as OpBreakPenalty control the relative weights of various
choices. BreakArith and its neighbors control whether the operator at a line break should be
placed at the end of the previous line or at the beginning of the next. If you don't want any
oversize lines, define MaxLineWidth =78.

Unlike TeX, p2c 's line breaker must actually try all possible sets of break points. To avoid
excessive computation, the total penalty contributed at each decision point must sum to a
nonnegative value; negative values are clipped up to zero. This allows p2c to prune away
obviously undesirable alternatives in advance. The MaxLineBreakTries parameter (default
5000) controls how many alternatives to try before giving up and using the best so far.

PASCAL_MAIN.
P2c generates a call to this function at the front of the main program. In the (unmodified) run-
time library all this does is save argc and argv away because in both HP and Turbo these are
accessed as global variables. If you do not wish to use this feature, define ArgCName to be
argc, ArgVName to be argv, and MainName (normally "PASCAL_MAIN") to be blank. This
will work if argc and argv are never accessed outside of your main program. BUGS P2c was
designed with the idea that clean, readable output in most cases is worth more than guaranteed
correct output in extreme cases. P2c is not a compiler! However, ideally the "extreme" cases
would include only those which never arise in real life. Thus if p2c actually generates incorrect
code I will consider it a bug, but I will not apologize for it. :-) Below are the major remaining
cases where this is known to occur.

Certain kinds of conformant array parameters (including multi-dimensional conformant arrays)
produce code that declares variable-length arrays in C. Only a few C compilers, such as the
GNU C compiler, support this language extension. Otherwise some hand re-coding will be
required.

HP Pascal try - recover structures are translated into calls to TRY and RECOVER macros,
which are defined to simulate the construct using setjmp and longjmp. If this emulation does not
work, define the symbol FAKE_TRY to cause these macros to become "inert." (In cases where
the error is detected by code physically within the body of the try statement, a C goto to the
recover section is always generated.) Also, local file variables in scopes which are destroyed by
an escape are not closed.

Non-local GOTO's and try - recover statements are each implemented, but may conflict if both
are used at once. Non-local GOTO's are fairly careful about closing files that go out of scope but
may fail to do so in the presence of recursion.

Arrays containing files are not initialized to NULL as other files are. In some cases, such as file
variables allocated by NEW, the file is initialized but not automatically closed by DISPOSE.

LINK variables allowing sub-procedures access to their parents' variables are occasionally
omitted by mistake, if the access is too indirect for p2c to notice. If this happens, you can add an
explicit reference to a parent variable in the sub-procedure. A statement of the form "a:=a" will
count as a reference but then be optimized away by p2c.

Many aspects of Modula-2 are translated only superficially. For example, the type-compatibility
properties of the WORD and ARRAY OF WORD types are only roughly modelled, as are the
scope rules concerning modules.

Parts of VAX Pascal are still untreated. In particular, the [UNSAFE] attribute and a few others
are not fully supported, nor are the semantics of the OPEN procedure.

Turbo and VAX Pascal's double, quadruple, and extended real types all translate to the C double
type. Turbo's computational type is not supported at all.

Because Pascal strings (with length bytes) are translated into C strings (with null terminators),
certain Pascal string tricks will not work in the translated code. For example the assignment
s[0]:=chr(x) is translated to s[x]=0 on the assumption that the string is being shortened. If x is
actually greater than the current length, but not of a recognizable form like ord(s[0])+n, then the
generated code will not work. In VAX Pascal this corresponds to performing arithmetic on the
LENGTH field of a varying-length string.

Turbo Pascal's automatic clipping of strings is not supported. In Turbo, if a ten character string
is assigned to a string[8] variable, the last two characters are silently removed. The code
produced by p2c generally will overrun the target string instead! The StringTruncLimit
parameter (80 by default if Language = Turbo ) specifies a string size which should be
considered "short"; assignments of potentially-long strings to short string variables will cause a
warning but will not automatically truncate. The cure is to use copy in the Pascal source to
truncate the strings explicitly.

FILES

file.xxx    Pascal source files r
file.c    resulting C source file
module.h    resulting C header file
p2c Preferences    local configuration file r
p2c Preferences    in the System preferences folder: system-wide configuration file r
system.imp    declarations for predefined functions
system.m2    analogous declarations for Modula-2
*.imp    interface text for standard modules; (mpw.imp for MPW)
p2c.h    header file for translated programs
libp2c.a    run-time library

AUTHOR
    Dave Gillespie, [e-mail].
    Günther Sawitzki, [e-mail]

Many thanks to William Bader, Steven Levi, Rick Koshi, Eric Raymond, Magne Haveraaen,
Dirk Grunwald, David Barto, Paul Fisher, Tom Schneider, and others whose suggestions and
bug reports have helped improve p2c in countless ways.

The original Unix version of p2c can be found on csvax.cs.caltech.edu.