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IRIX Base Documentation 1998 November
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IRIX 6.5.2 Base Documentation November 1998.img
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catman
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u_man
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cat1
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ctrace.z
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ctrace
Wrap
Text File
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1998-10-30
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15KB
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330 lines
CCCCTTTTRRRRAAAACCCCEEEE((((1111)))) SSSSiiiilllliiiiccccoooonnnn GGGGrrrraaaapppphhhhiiiiccccssss CCCCTTTTRRRRAAAACCCCEEEE((((1111))))
NNNNAAAAMMMMEEEE
ctrace - C program debugger
SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS
ccccttttrrrraaaacccceeee [options] [file]
DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
The _c_t_r_a_c_e command allows you to follow the execution of a C program,
statement-by-statement. The effect is similar to executing a shell
procedure with the ----xxxx option. _c_t_r_a_c_e reads the C program in _f_i_l_e (or
from standard input if you do not specify _f_i_l_e), inserts statements to
print the text of each executable statement and the values of all
variables referenced or modified, and writes the modified program to the
standard output. You must put the output of _c_t_r_a_c_e into a temporary file
because the _c_c(1) command does not allow the use of a pipe. You then
compile and execute this file.
As each statement in the program executes it will be listed at the
terminal, followed by the name and value of any variables referenced or
modified in the statement, followed by any output from the statement.
Loops in the trace output are detected and tracing is stopped until the
loop is exited or a different sequence of statements within the loop is
executed. A warning message is printed every 1000 times through the loop
to help you detect infinite loops. The trace output goes to the standard
output so you can put it into a file for examination with an editor or
the _b_f_s(1) or _t_a_i_l(1) commands.
The options commonly used are:
----ffff _f_u_n_c_t_i_o_n_s Trace only these _f_u_n_c_t_i_o_n_s.
----vvvv _f_u_n_c_t_i_o_n_s Trace all but these _f_u_n_c_t_i_o_n_s.
You may want to add to the default formats for printing variables. Long
and pointer variables are always printed as signed integers. Pointers to
character arrays are also printed as strings if appropriate. Char,
short, and int variables are also printed as signed integers and, if
appropriate, as characters. Double variables are printed as floating
point numbers in scientific notation. You can request that variables be
printed in additional formats, if appropriate, with these options:
----oooo Octal
----xxxx Hexadecimal
----uuuu Unsigned
----eeee Floating point
These options are used only in special circumstances:
----llll _n Check _n consecutively executed statements for looping trace
output, instead of the default of 20. Use 0 to get all the trace
output from loops.
Page 1 Release 6.4
CCCCTTTTRRRRAAAACCCCEEEE((((1111)))) SSSSiiiilllliiiiccccoooonnnn GGGGrrrraaaapppphhhhiiiiccccssss CCCCTTTTRRRRAAAACCCCEEEE((((1111))))
----ssss Suppress redundant trace output from simple assignment statements
and string copy function calls. This option can hide a bug caused
by use of the = operator in place of the == operator.
----tttt _n Trace _n variables per statement instead of the default of 10 (the
maximum number is 20). The Diagnostics section explains when to
use this option.
----PPPP Run the C preprocessor on the input before tracing it. You can
also use the ----DDDD, ----IIII, and ----UUUU _c_p_p(1) options.
These options are used to tailor the run-time trace package when the
traced program will run in a non-UNIX System environment:
----bbbb Use only basic functions in the trace code, that is, those in
_c_t_y_p_e(3C), _p_r_i_n_t_f(3S), and _s_t_r_i_n_g(3C). These are usually
available even in cross-compilers for microprocessors. In
particular, this option is needed when the traced program runs
under an operating system that does not have _s_i_g_n_a_l(2),
_f_f_l_u_s_h(3S), _l_o_n_g_j_m_p(3C), or _s_e_t_j_m_p(3C).
----pppp _s_t_r_i_n_g
Change the trace print function from the default of 'printf('.
For example, 'fprintf(stderr,' would send the trace to the
standard error output.
----rrrr _f Use file _f in place of the _r_u_n_t_i_m_e._c trace function package. This
lets you change the entire print function, instead of just the
name and leading arguments (see the ----pppp option).
EEEEXXXXAAAAMMMMPPPPLLLLEEEE
If the file _l_c._c contains this C program:
1 #include <stdio.h>
2 main() /* count lines in input */
3 {
4 int c, nl;
5
6 nl = 0;
7 while ((c = getchar()) != EOF)
8 if (c = '\n')
9 ++nl;
10 printf("%d\n", nl);
11 }
and you enter these commands and test data:
cc lc.c
a.out
1
(cntl-d)
the program will be compiled and executed. The output of the program
will be the number 2222, which is not correct because there is only one line
in the test data. The error in this program is common, but subtle. If
you invoke _c_t_r_a_c_e with these commands:
ctrace lc.c >temp.c
cc temp.c
a.out
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CCCCTTTTRRRRAAAACCCCEEEE((((1111)))) SSSSiiiilllliiiiccccoooonnnn GGGGrrrraaaapppphhhhiiiiccccssss CCCCTTTTRRRRAAAACCCCEEEE((((1111))))
the output will be:
2 main()
6 nl = 0;
/* nl == 0 */
7 while ((c = getchar()) != EOF)
The program is now waiting for input. If you enter the same test data as
before, the output will be:
/* c == 49 or '1' */
8 if (c = '\n')
/* c == 10 or '\n' */
9 ++nl;
/* nl == 1 */
7 while ((c = getchar()) != EOF)
/* c == 10 or '\n' */
8 if (c = '\n')
/* c == 10 or '\n' */
9 ++nl;
/* nl == 2 */
7 while ((c = getchar()) != EOF)
If you now enter an end of file character (cntl-d) the final output will
be:
/* c == -1 */
10 printf("%d\n", nl);
/* nl == 2 */2
return
Note that the program output printed at the end of the trace line for the
nnnnllll variable. Also note the rrrreeeettttuuuurrrrnnnn comment added by _c_t_r_a_c_e at the end of
the trace output. This shows the implicit return at the terminating
brace in the function.
The trace output shows that variable cccc is assigned the value '1' in line
7, but in line 8 it has the value '\n'. Once your attention is drawn to
this iiiiffff statement, you will probably realize that you used the assignment
operator (=) in place of the equality operator (==). You can easily miss
this error during code reading.
EEEEXXXXEEEECCCCUUUUTTTTIIIIOOOONNNN----TTTTIIIIMMMMEEEE TTTTRRRRAAAACCCCEEEE CCCCOOOONNNNTTTTRRRROOOOLLLL
The default operation for _c_t_r_a_c_e is to trace the entire program file,
unless you use the ----ffff or ----vvvv options to trace specific functions. This
does not give you statement-by-statement control of the tracing, nor does
it let you turn the tracing off and on when executing the traced program.
You can do both of these by adding _c_t_r_o_f_f() and _c_t_r_o_n() function calls to
your program to turn the tracing off and on, respectively, at execution
time. Thus, you can code arbitrarily complex criteria for trace control
with _i_f statements, and you can even conditionally include this code
because _c_t_r_a_c_e defines the CCCCTTTTRRRRAAAACCCCEEEE preprocessor variable. For example:
#ifdef CTRACE
if (c == '!' && i > 1000)
ctron();
#endif
Page 3 Release 6.4
CCCCTTTTRRRRAAAACCCCEEEE((((1111)))) SSSSiiiilllliiiiccccoooonnnn GGGGrrrraaaapppphhhhiiiiccccssss CCCCTTTTRRRRAAAACCCCEEEE((((1111))))
You can also control tracing from _d_b_x(1) if you compile with the ----gggg
option by turning trace on and off with the static variable tr_ct_.. For
example, to trace all but lines 7 to 10 in the main function, enter:
dbx a.out
when at 7 { assign tr_ct_ = 0 }
when at 11 { assign tr_ct_ = 1 }
run
DDDDIIIIAAAAGGGGNNNNOOOOSSSSTTTTIIIICCCCSSSS
This section contains diagnostic messages from both _c_t_r_a_c_e and _c_c(1),
since the traced code often gets some _c_c warning messages. You can get
_c_c error messages in some rare cases, all of which can be avoided.
ccccttttrrrraaaacccceeee DDDDiiiiaaaaggggnnnnoooossssttttiiiiccccssss
_w_a_r_n_i_n_g: _s_o_m_e _v_a_r_i_a_b_l_e_s _a_r_e _n_o_t _t_r_a_c_e_d _i_n _t_h_i_s _s_t_a_t_e_m_e_n_t
Only 10 variables are traced in a statement to prevent the C
compiler "out of tree space; simplify expression" error. Use the ----tttt
option to increase this number.
_w_a_r_n_i_n_g: _s_t_a_t_e_m_e_n_t _t_o_o _l_o_n_g _t_o _t_r_a_c_e
This statement is over 400 characters long. Make sure that you are
using tabs to indent your code, not spaces.
_c_a_n_n_o_t _h_a_n_d_l_e _p_r_e_p_r_o_c_e_s_s_o_r _c_o_d_e, _u_s_e -_P _o_p_t_i_o_n
This is usually caused by #ifdef/#endif preprocessor statements in
the middle of a C statement, or by a semicolon at the end of a
#define preprocessor statement.
'_i_f ... _e_l_s_e _i_f' _s_e_q_u_e_n_c_e _t_o_o _l_o_n_g
Split the sequence by removing an eeeellllsssseeee from the middle.
_p_o_s_s_i_b_l_e _s_y_n_t_a_x _e_r_r_o_r, _t_r_y -_P _o_p_t_i_o_n
Use the ----PPPP option to preprocess the _c_t_r_a_c_e input, along with any
appropriate ----DDDD, ----IIII, and ----UUUU preprocessor options. If you still get
the error message, check the Warnings section below.
CCCCcccc DDDDiiiiaaaaggggnnnnoooossssttttiiiiccccssss
_w_a_r_n_i_n_g: _i_l_l_e_g_a_l _c_o_m_b_i_n_a_t_i_o_n _o_f _p_o_i_n_t_e_r _a_n_d _i_n_t_e_g_e_r
_w_a_r_n_i_n_g: _s_t_a_t_e_m_e_n_t _n_o_t _r_e_a_c_h_e_d
_w_a_r_n_i_n_g: _s_i_z_e_o_f _r_e_t_u_r_n_s _0
Ignore these messages.
_c_o_m_p_i_l_e_r _t_a_k_e_s _s_i_z_e _o_f _f_u_n_c_t_i_o_n
See the _c_t_r_a_c_e "possible syntax error" message above.
_y_a_c_c _s_t_a_c_k _o_v_e_r_f_l_o_w
See the _c_t_r_a_c_e "'if ... else if' sequence too long" message above.
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CCCCTTTTRRRRAAAACCCCEEEE((((1111)))) SSSSiiiilllliiiiccccoooonnnn GGGGrrrraaaapppphhhhiiiiccccssss CCCCTTTTRRRRAAAACCCCEEEE((((1111))))
_o_u_t _o_f _t_r_e_e _s_p_a_c_e; _s_i_m_p_l_i_f_y _e_x_p_r_e_s_s_i_o_n
Use the ----tttt option to reduce the number of traced variables per
statement from the default of 10. Ignore the "ctrace: too many
variables to trace" warnings you will now get.
_r_e_d_e_c_l_a_r_a_t_i_o_n _o_f _s_i_g_n_a_l
Either correct this declaration of _s_i_g_n_a_l(2), or remove it and
#include <signal.h>.
SSSSEEEEEEEE AAAALLLLSSSSOOOO
bfs(1), dbx(1), tail(1), signal(2), ctype(3C), fclose(3S), printf(3S),
setjmp(3C), string(3C).
WWWWAAAARRRRNNNNIIIINNNNGGGGSSSS
You will get a _c_t_r_a_c_e syntax error if you omit the semicolon at the end
of the last element declaration in a structure or union, just before the
right brace (}). This is optional in some C compilers.
Defining a function with the same name as a system function may cause a
syntax error if the number of arguments is changed. Just use a different
name.
_c_t_r_a_c_e assumes that BADMAG is a preprocessor macro, and that EOF and NULL
are #defined constants. Declaring any of these to be variables, e.g.,
"int EOF;", will cause a syntax error.
BBBBUUUUGGGGSSSS
_c_t_r_a_c_e does not know about the components of aggregates like structures,
unions, and arrays. It cannot choose a format to print all the
components of an aggregate when an assignment is made to the entire
aggregate. _c_t_r_a_c_e may choose to print the address of an aggregate or use
the wrong format (e.g., 3.149050e-311 for a structure with two integer
members) when printing the value of an aggregate.
Pointer values are always treated as pointers to character strings.
The loop trace output elimination is done separately for each file of a
multi-file program. This can result in functions called from a loop
still being traced, or the elimination of trace output from one function
in a file until another in the same file is called.
FFFFIIIILLLLEEEESSSS
/usr/lib/ctrace/runtime.c run-time trace package
Page 5 Release 6.4
