SYNOPSIS
int printf(const char *format, /* args*/ ...);
int sprintf(char *s, const char *format, /* args*/ ...);
The printf() function places output on the output stream stdout.
The sprintf() function places output, followed by the null byte (\0),
in consecutive bytes starting at s; the CScript engine ensures
that enough storage is available.
Each of these functions converts, formats, and prints its args
under control of the format. The format is a character
string, beginning and ending in its initial shift state, if any.
The format is composed of zero or more directives defined as follows:
- ordinary characters, which are simply copied to the
output stream;
- escape sequences, which represent non-graphic characters;
and
- conversion specifications, each of which results in the
fetching of zero or more arguments.
The results are undefined if there are insufficient arguments for the
format. If the format is exhausted while arguments remain,
the excess arguments are evaluated but are otherwise ignored.
Conversions can be applied to the nth argument after the
format in the argument list, rather than to the next unused
argument. In this case, the conversion character % (see below) is
replaced by the sequence %n$, where n is a decimal integer
in the range [1, NL_ARGMAX], giving the position of
the argument in the argument list. This feature provides for
the definition of format strings that select arguments in an
order appropriate to specific languages (see the EXAMPLES section).
In format strings containing the %n$ form of conversion
specifications, numbered arguments in the argument list can
be referenced from the format string as many times as
required.
In format strings containing the % form of conversion
specifications, each argument in the argument list is used
exactly once.
Escape Sequences
The following escape sequences produce the associated action
on display devices capable of the action:
- \n Newline. Move the printing position to the start
of the next line.
- \r Carriage return. Move the printing position to the
start of the current line.
- \t Horizontal tab. Move the printing position to the
next implementation-defined horizontal tab position on the current line.
Conversion Specifications
Each conversion specification is introduced by the character
% or by the character sequence %n$, after which the following
appear in sequence:
- An optional field, consisting of a decimal digit
string followed by a $, specifying the next args to be
converted. If this field is not provided, the args
following the last args converted will be used.
- Zero or more flags (in any order), which modify the
meaning of the conversion specification.
- An optional minimum field width. If the converted
value has fewer bytes than the field width, it will be
padded with spaces by default on the left; it will be
padded on the right, if the left-adjustment flag (-),
described below, is given to the field width. The
field width takes the form of an asterisk (*),
described below, or a decimal integer.
If the conversion character is s, a standard-conforming
application interprets the field width as the
minimum number of
bytes to be printed; an application that is not
standard-conforming interprets the field width as
the minimum number of columns of screen display.
For an application that is not standard-
conforming, %10s means if the converted value has
a screen width of 7 columns, 3 spaces would be
padded on the right.
If the format is %ws, then the field width should
be interpreted as the minimum number of columns
of screen display.
- An optional precision that gives the minimum number of
digits to appear for the d, i, o, u, x, or X conversions (the field
is padded with leading zeros); the
number of digits to appear after the radix character
for the e, E, and f conversions, the maximum number of
significant digits for the g and G conversions; or the
maximum number of bytes to be printed from a string in
s and S conversions. The precision takes the form of
a period (.) followed either by an asterisk (*),
described below, or an optional decimal digit string,
where a null digit string is treated as 0. If a precision
appears with any other conversion character,
the behavior is undefined.
If the conversion character is s or S, a
standard-conforming application interprets the precision
as the maximum number of bytes to be written; an application that is not
standard-conforming interprets the precision as
the maximum number of columns of screen display.
For an application that is not standard-conforming,
%.5s would print only the portion of
the string that would display in 5 screen columns.
Only complete characters are written.
For %ws, the precision should be interpreted as
the maximum number of columns of screen display.
The precision takes the form of a period (.) followed by a
decimal digit string; a null digit
string is treated as zero. Padding specified by
the precision overrides the padding specified by
the field width.
- An optional h specifies that a following d, i, o, u,
x, or X conversion character applies to a type short
int or unsigned short int argument (the argument will
be promoted according to the integral promotions and
its value converted to type short int or unsigned
short int before printing); an optional h specifies
that a following n conversion character applies to a
pointer to a type short int argument. An optional l
(ell) specifies that a following d, i, o, u, x, or X
conversion character applies to a type long int or
unsigned long int argument; an optional l (ell)
specifies that a following n conversion character
applies to a pointer to a type long int argument. An
optional ll (ell ell) specifies that a following d,
i, o, u, x, or X conversion character applies to a
type long long or unsigned long long argument; an
optional ll (ell ell) specifies that a following n
conversion character applies to a pointer to a long
long argument. An optional L specifies that a following
e, E, f, g, or G conversion character applies to a
long double argument. If an h, l, or L appears before
any other conversion character, the behavior is undefined.
- A conversion character (see below) that indicates the
type of conversion to be applied.
A field width or precision may be indicated by an asterisk
(*) instead of a digit string. In this case, an integer args
supplies the field width or precision. The args that is
actually converted is not fetched until the conversion
letter is seen, so the args specifying field width or precision
must appear before the args (if any) to be converted.
If the precision argument is negative, it will be changed to
zero. A negative field width argument is taken as a - flag,
followed by a positive field width. A negative precision is
taken as if the precision were omitted. In format strings
containing the %n$ form of a conversion specification, a
field width or precision may be indicated by the sequence
*m$, where m is a decimal integer in the range [1,
NL_ARGMAX] giving the position in the argument list (after
the format argument) of an integer argument containing the
field width or precision, for example:
printf("%1$d:%2$.*3$d:%4$.*3$d\n", hour, min, precision, sec);
The format can contain either numbered argument specifications
(that is, %n$ and *m$), or unnumbered argument specifications
(that is, % and *), but normally not both. The only exception to this
is that %% can be mixed with the %n$ form. The results of mixing
numbered and unnumbered argument specifications in a format
string are undefined. When numbered argument specifications are used,
specifying the Nth argument requires that all the leading
arguments, from the first to the (N-1)th, are specified in
the format string.
Flag Characters
The flag characters and their meanings are:
- ' The integer portion of the result of a decimal
conversion (%i, %d, %u, %f, %g, or %G) will be
formatted with thousands' grouping characters. For
other conversions the behavior is undefined. The
non-monetary grouping character is used.
- - The result of the conversion will be left-justified
within the field. (It will be right-justified if this flag is not
specified.)
- + The result of a signed conversion will always
begin with a sign (+ or -). (It will begin with a
sign only when a negative value is converted if
this flag is not specified.)
- space If the first character of a signed conversion is
not a sign, a space will be placed before the
result. This means that if the space and + flags
both appear, the space flag will be ignored.
- # The value is to be converted to an alternate form.
For c, d, i, s, and u conversions, the flag has no
effect. For an o conversion, it increases the precision to
force the first digit of the result to be a zero.
For x (or X) conversion, a non-zero
result will have 0x (or 0X) prepended to it. For
e, E, f, g, and G conversions, the result will
always contain a radix character, even if no
digits follow the point (normally, a decimal point
appears in the result of these conversions only if
a digit follows it). For g and G conversions,
trailing zeros will not be removed from the result
as they normally are.
- 0 For d, i, o, u, x, X, e, E, f, g, and G conversions,
leading zeros (following any indication of
sign or base) are used to pad to the field width;
no space padding is performed. If the 0 and -
flags both appear, the 0 flag will be ignored. For
d, i, o, u, x, and X conversions, if a precision
is specified, the 0 flag will be ignored. For
other conversions, the behavior is undefined.
Conversion Characters
Each conversion character results in fetching zero or more
args. The results are undefined if there are insufficient
args for the format. If the format is exhausted while args
remain, the excess args are ignored.
The conversion characters and their meanings are:
- d,i The int argument is converted to a signed decimal
in the style [-]dddd. The precision specifies the
minimum number of digits to appear; if the value
being converted can be represented in fewer
digits, it will be expanded with leading zeros.
The default precision is 1. The result of converting 0
with an explicit precision of 0 is no characters.
- o The unsigned int argument is converted to unsigned
octal format in the style dddd. The precision
specifies the minimum number of digits to appear;
if the value being converted can be represented in
fewer digits, it will be expanded with leading
zeros. The default precision is 1. The result of
converting 0 with an explicit precision of 0 is no
characters.
- u The unsigned int argument is converted to unsigned
decimal format in the style dddd. The precision
specifies the minimum number of digits to appear;
if the value being converted can be represented in
fewer digits, it will be expanded with leading
zeros. The default precision is 1. The result of
converting 0 with an explicit precision of 0 is no
characters.
- x The unsigned int argument is converted to unsigned
hexadecimal format in the style dddd; the letters
abcdef are used. The precision specifies the
minimum number of digits to appear; if the value
being converted can be represented in fewer
digits, it will be expanded with leading zeros.
The default precision is 1. The result of converting
ing 0 with an explicit precision of 0 is no characters.
- X Behaves the same as the x conversion character
except that letters ABCDEF are used instead of abcdef.
- f The double args is converted to decimal notation
in the style [-]ddd.ddd, where the number of
digits after the radix character
is equal to the precision specification. If the precision is
omitted from arg, six
digits are output; if the precision is explicitly
zero and the # flag is not specified, no radix
character appears. If a radix character appears,
at least 1 digit appears before it. The value is
rounded to the appropriate number of digits.
- e,E The double args is converted to the style
[-]d.ddde_dd, where there is one digit before the
radix character (which is non-zero if the argument
is non-zero) and the number of digits after it is
equal to the precision. When the precision is
missing, six digits are produced; if the precision
is zero and the # flag is not specified, no radix
character appears. The E conversion character
will produce a number with E instead of e introducing the
exponent. The exponent always contains
at least two digits. The value is rounded to the
appropriate number of digits.
- g,G The double args is printed in style f or e (or in
style E in the case of a G conversion character),
with the precision specifying the number of significant digits.
If the precision is zero, it is
taken as one. The style used depends on the value
converted: style e (or E) will be used only if the
exponent resulting from the conversion is less
than -4 or greater than or equal to the precision.
Trailing zeros are removed from the fractional
part of the result. A radix character appears only
if it is followed by a digit.
- c The int args is converted to an unsigned char, and
the resulting byte is printed.
- s The args is taken to be a string (character
pointer) and characters from the string are written
up to (but not including) a terminating null
byte. If a precision is specified, a standard-conforming application
will write only the number of bytes specified by precision; an
application that is not standard-conforming will write only
the portion of the string that will display in the number of columns
of screen display specified by precision.
If the precision is not specified, it is taken to
be infinite, so all bytes up to the first null
byte are printed. A null value for args will yield
undefined results.
- % Print a %; no argument is converted. The entire
conversion specification must be %%.
If a conversion specification does not match one of the
above forms, the behavior is undefined.
If a floating-point value is the internal representation for
infinity, the output is [_]Infinity, where Infinity
is either Infinity or Inf, depending on the desired output
string length. Printing of the sign follows the rules
described above.
If a floating-point value is the internal representation for
"not-a-number," the output is [_]NaN. Printing of the sign
follows the rules described above.
In no case does a non-existent or small field width cause
truncation of a field; if the result of a conversion is
wider than the field width, the field is simply expanded to
contain the conversion result. Characters generated by
printf() are printed as if the function had been called.
RETURN VALUES
The printf() and sprintf() functions return the number of bytes
transmitted (not including the \0 in the case of sprintf()). The
snprintf() function returns the number of characters formatted,
that is, the number of characters that were written to the buffer.
Each function returns a negative value if an output error was encountered.
EXAMPLES
Example 1: To print the language-independent date and time
format, the following statement could be used:
printf (format, weekday, month, day, hour, min);
For American usage, format could be a pointer to the string:
"%s, %s %d, %d:%.2d\n"
producing the message:
Sunday, July 3, 10:02
whereas for German usage, format could be a pointer to the string:
"%1$s, %3$d. %2$s, %4$d:%5$.2d\n"
producing the message:
Sonntag, 3. Juli, 10:02
Example 2: To print a date and time in the form Sunday, July
3, 10:02, where weekday and month are pointers to null-terminated strings:
printf("%s, %s %i, %d:%.2d", weekday, month, day, hour, min);
Example 3: To print pi to 5 decimal places:
printf("pi = %.5f", 4 * atan(1.0));