FPRINTF(3P) POSIX Programmer's Manual FPRINTF(3P)
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This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
Linux manual page for details of Linux behavior), or the interface may
not be implemented on Linux.
NAME
dprintf, fprintf, printf, snprintf, sprintf -- print formatted output
SYNOPSIS
#include <stdio.h>
int dprintf(int fildes, const char *restrict format, ...);
int fprintf(FILE *restrict stream, const char *restrict format, ...);
int printf(const char *restrict format, ...);
int snprintf(char *restrict s, size_t n,
const char *restrict format, ...);
int sprintf(char *restrict s, const char *restrict format, ...);
DESCRIPTION
Excluding dprintf(): The functionality described on this reference page
is aligned with the ISO C standard. Any conflict between the require-
ments described here and the ISO C standard is unintentional. This vol-
ume of POSIX.1-2008 defers to the ISO C standard.
The fprintf() function shall place output on the named output stream.
The printf() function shall place output on the standard output stream
stdout. The sprintf() function shall place output followed by the null
byte, '\0', in consecutive bytes starting at *s; it is the user's
responsibility to ensure that enough space is available.
The dprintf() function shall be equivalent to the fprintf() function,
except that dprintf() shall write output to the file associated with
the file descriptor specified by the fildes argument rather than place
output on a stream.
The snprintf() function shall be equivalent to sprintf(), with the
addition of the n argument which states the size of the buffer referred
to by s. If n is zero, nothing shall be written and s may be a null
pointer. Otherwise, output bytes beyond the n-1st shall be discarded
instead of being written to the array, and a null byte is written at
the end of the bytes actually written into the array.
If copying takes place between objects that overlap as a result of a
call to sprintf() or snprintf(), the results are undefined.
Each of these functions converts, formats, and prints its arguments
under control of the format. The format is a character string, begin-
ning and ending in its initial shift state, if any. The format is com-
posed of zero or more directives: ordinary characters, which are simply
copied to the output stream, and conversion specifications, each of
which shall result in the fetching of zero or more arguments. The
results are undefined if there are insufficient arguments for the for-
mat. If the format is exhausted while arguments remain, the excess
arguments shall be 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 specifier character % (see below) is replaced by the
sequence "%n$", where n is a decimal integer in the range
[1,{NL_ARGMAX}], giving the position of the argument in the argument
list. This feature provides for the definition of format strings that
select arguments in an order appropriate to specific languages (see the
EXAMPLES section).
The format can contain either numbered argument conversion specifica-
tions (that is, "%n$" and "*m$"), or unnumbered argument conversion
specifications (that is, % and *), but not both. The only exception to
this is that %% can be mixed with the "%n$" 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.
In format strings containing the "%n$" form of conversion specifica-
tion, numbered arguments in the argument list can be referenced from
the format string as many times as required.
In format strings containing the % form of conversion specification,
each conversion specification uses the first unused argument in the
argument list.
All forms of the fprintf() functions allow for the insertion of a lan-
guage-dependent radix character in the output string. The radix charac-
ter is defined in the current locale (category LC_NUMERIC). In the
POSIX locale, or in a locale where the radix character is not defined,
the radix character shall default to a <period> ('.').
Each conversion specification is introduced by the '%' character or by
the character sequence "%n$", after which the following appear in
sequence:
* 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 shall be padded with <space> charac-
ters by default on the left; it shall 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.
* An optional precision that gives the minimum number of digits to
appear for the d, i, o, u, x, and X conversion specifiers; the num-
ber of digits to appear after the radix character for the a, A, e,
E, f, and F conversion specifiers; the maximum number of signifi-
cant digits for the g and G conversion specifiers; or the maximum
number of bytes to be printed from a string in the s and S conver-
sion specifiers. 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 zero. If a precision appears with any other conversion speci-
fier, the behavior is undefined.
* An optional length modifier that specifies the size of the argu-
ment.
* A conversion specifier character that indicates the type of conver-
sion to be applied.
A field width, or precision, or both, may be indicated by an <asterisk>
('*'). In this case an argument of type int supplies the field width
or precision. Applications shall ensure that arguments specifying field
width, or precision, or both appear in that order before the argument,
if any, to be converted. A negative field width 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 flag characters and their meanings are:
' (The <apostrophe>.) The integer portion of the result of a
decimal conversion (%i, %d, %u, %f, %F, %g, or %G) shall be
formatted with thousands' grouping characters. For other con-
versions the behavior is undefined. The non-monetary grouping
character is used.
- The result of the conversion shall be left-justified within the
field. The conversion is right-justified if this flag is not
specified.
+ The result of a signed conversion shall always begin with a
sign ('+' or '-'). The conversion shall begin with a sign only
when a negative value is converted if this flag is not speci-
fied.
<space> If the first character of a signed conversion is not a sign or
if a signed conversion results in no characters, a <space>
shall be prefixed to the result. This means that if the <space>
and '+' flags both appear, the <space> flag shall be ignored.
# Specifies that the value is to be converted to an alternative
form. For o conversion, it increases the precision (if neces-
sary) to force the first digit of the result to be zero. For x
or X conversion specifiers, a non-zero result shall have 0x (or
0X) prefixed to it. For a, A, e, E, f, F, g, and G conversion
specifiers, the result shall always contain a radix character,
even if no digits follow the radix character. Without this
flag, a radix character appears in the result of these conver-
sions only if a digit follows it. For g and G conversion speci-
fiers, trailing zeros shall not be removed from the result as
they normally are. For other conversion specifiers, the behav-
ior is undefined.
0 For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversion
specifiers, leading zeros (following any indication of sign or
base) are used to pad to the field width rather than performing
space padding, except when converting an infinity or NaN. If
the '0' and '-' flags both appear, the '0' flag is ignored. For
d, i, o, u, x, and X conversion specifiers, if a precision is
specified, the '0' flag shall be ignored. If the '0' and
<apostrophe> flags both appear, the grouping characters are
inserted before zero padding. For other conversions, the behav-
ior is undefined.
The length modifiers and their meanings are:
hh Specifies that a following d, i, o, u, x, or X conversion spec-
ifier applies to a signed char or unsigned char argument (the
argument will have been promoted according to the integer pro-
motions, but its value shall be converted to signed char or
unsigned char before printing); or that a following n conver-
sion specifier applies to a pointer to a signed char argument.
h Specifies that a following d, i, o, u, x, or X conversion spec-
ifier applies to a short or unsigned short argument (the argu-
ment will have been promoted according to the integer promo-
tions, but its value shall be converted to short or unsigned
short before printing); or that a following n conversion speci-
fier applies to a pointer to a short argument.
l (ell) Specifies that a following d, i, o, u, x, or X conversion spec-
ifier applies to a long or unsigned long argument; that a fol-
lowing n conversion specifier applies to a pointer to a long
argument; that a following c conversion specifier applies to a
wint_t argument; that a following s conversion specifier
applies to a pointer to a wchar_t argument; or has no effect on
a following a, A, e, E, f, F, g, or G conversion specifier.
ll (ell-ell)
Specifies that a following d, i, o, u, x, or X conversion spec-
ifier applies to a long long or unsigned long long argument; or
that a following n conversion specifier applies to a pointer to
a long long argument.
j Specifies that a following d, i, o, u, x, or X conversion spec-
ifier applies to an intmax_t or uintmax_t argument; or that a
following n conversion specifier applies to a pointer to an
intmax_t argument.
z Specifies that a following d, i, o, u, x, or X conversion spec-
ifier applies to a size_t or the corresponding signed integer
type argument; or that a following n conversion specifier
applies to a pointer to a signed integer type corresponding to
a size_t argument.
t Specifies that a following d, i, o, u, x, or X conversion spec-
ifier applies to a ptrdiff_t or the corresponding unsigned type
argument; or that a following n conversion specifier applies to
a pointer to a ptrdiff_t argument.
L Specifies that a following a, A, e, E, f, F, g, or G conversion
specifier applies to a long double argument.
If a length modifier appears with any conversion specifier other than
as specified above, the behavior is undefined.
The conversion specifiers and their meanings are:
d, i The int argument shall be 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 repre-
sented in fewer digits, it shall be expanded with leading
zeros. The default precision is 1. The result of converting
zero with an explicit precision of zero shall be no characters.
o The unsigned argument shall be converted to unsigned octal for-
mat 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 shall be expanded with leading
zeros. The default precision is 1. The result of converting
zero with an explicit precision of zero shall be no characters.
u The unsigned argument shall be 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 shall be expanded with leading
zeros. The default precision is 1. The result of converting
zero with an explicit precision of zero shall be no characters.
x The unsigned argument shall be converted to unsigned hexadeci-
mal 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 dig-
its, it shall be expanded with leading zeros. The default pre-
cision is 1. The result of converting zero with an explicit
precision of zero shall be no characters.
X Equivalent to the x conversion specifier, except that letters
"ABCDEF" are used instead of "abcdef".
f, F The double argument shall be 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 missing, it shall be taken as 6; if the precision
is explicitly zero and no '#' flag is present, no radix charac-
ter shall appear. If a radix character appears, at least one
digit appears before it. The low-order digit shall be rounded
in an implementation-defined manner.
A double argument representing an infinity shall be converted
in one of the styles "[-]inf" or "[-]infinity"; which style is
implementation-defined. A double argument representing a NaN
shall be converted in one of the styles "[-]nan(n-char-
sequence)" or "[-]nan"; which style, and the meaning of any n-
char-sequence, is implementation-defined. The F conversion
specifier produces "INF", "INFINITY", or "NAN" instead of
"inf", "infinity", or "nan", respectively.
e, E The double argument shall be converted in 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; if the
precision is missing, it shall be taken as 6; if the precision
is zero and no '#' flag is present, no radix character shall
appear. The low-order digit shall be rounded in an implementa-
tion-defined manner. The E conversion specifier shall produce a
number with 'E' instead of 'e' introducing the exponent. The
exponent shall always contain at least two digits. If the value
is zero, the exponent shall be zero.
A double argument representing an infinity or NaN shall be con-
verted in the style of an f or F conversion specifier.
g, G The double argument representing a floating-point number shall
be converted in the style f or e (or in the style F or E in the
case of a G conversion specifier), depending on the value con-
verted and the precision. Let P equal the precision if non-
zero, 6 if the precision is omitted, or 1 if the precision is
zero. Then, if a conversion with style E would have an exponent
of X:
-- If P>X>=-4, the conversion shall be with style f (or F) and
precision P-(X+1).
-- Otherwise, the conversion shall be with style e (or E) and
precision P-1.
Finally, unless the '#' flag is used, any trailing zeros shall
be removed from the fractional portion of the result and the
decimal-point character shall be removed if there is no frac-
tional portion remaining.
A double argument representing an infinity or NaN shall be con-
verted in the style of an f or F conversion specifier.
a, A A double argument representing a floating-point number shall be
converted in the style "[-]0xh.hhhhp+-d", where there is one
hexadecimal digit (which shall be non-zero if the argument is a
normalized floating-point number and is otherwise unspecified)
before the decimal-point character and the number of hexadeci-
mal digits after it is equal to the precision; if the precision
is missing and FLT_RADIX is a power of 2, then the precision
shall be sufficient for an exact representation of the value;
if the precision is missing and FLT_RADIX is not a power of 2,
then the precision shall be sufficient to distinguish values of
type double, except that trailing zeros may be omitted; if the
precision is zero and the '#' flag is not specified, no deci-
mal-point character shall appear. The letters "abcdef" shall be
used for a conversion and the letters "ABCDEF" for A conver-
sion. The A conversion specifier produces a number with 'X' and
'P' instead of 'x' and 'p'. The exponent shall always contain
at least one digit, and only as many more digits as necessary
to represent the decimal exponent of 2. If the value is zero,
the exponent shall be zero.
A double argument representing an infinity or NaN shall be con-
verted in the style of an f or F conversion specifier.
c The int argument shall be converted to an unsigned char, and
the resulting byte shall be written.
If an l (ell) qualifier is present, the wint_t argument shall
be converted as if by an ls conversion specification with no
precision and an argument that points to a two-element array of
type wchar_t, the first element of which contains the wint_t
argument to the ls conversion specification and the second ele-
ment contains a null wide character.
s The argument shall be a pointer to an array of char. Bytes
from the array shall be written up to (but not including) any
terminating null byte. If the precision is specified, no more
than that many bytes shall be written. If the precision is not
specified or is greater than the size of the array, the appli-
cation shall ensure that the array contains a null byte.
If an l (ell) qualifier is present, the argument shall be a
pointer to an array of type wchar_t. Wide characters from the
array shall be converted to characters (each as if by a call to
the wcrtomb() function, with the conversion state described by
an mbstate_t object initialized to zero before the first wide
character is converted) up to and including a terminating null
wide character. The resulting characters shall be written up to
(but not including) the terminating null character (byte). If
no precision is specified, the application shall ensure that
the array contains a null wide character. If a precision is
specified, no more than that many characters (bytes) shall be
written (including shift sequences, if any), and the array
shall contain a null wide character if, to equal the character
sequence length given by the precision, the function would need
to access a wide character one past the end of the array. In no
case shall a partial character be written.
p The argument shall be a pointer to void. The value of the
pointer is converted to a sequence of printable characters, in
an implementation-defined manner.
n The argument shall be a pointer to an integer into which is
written the number of bytes written to the output so far by
this call to one of the fprintf() functions. No argument is
converted.
C Equivalent to lc.
S Equivalent to ls.
% Print a '%' character; no argument is converted. The complete
conversion specification shall be %%.
If a conversion specification does not match one of the above forms,
the behavior is undefined. If any argument is not the correct type for
the corresponding conversion specification, the behavior is undefined.
In no case shall a nonexistent or small field width cause truncation of
a field; if the result of a conversion is wider than the field width,
the field shall be expanded to contain the conversion result. Charac-
ters generated by fprintf() and printf() are printed as if fputc() had
been called.
For the a and A conversion specifiers, if FLT_RADIX is a power of 2,
the value shall be correctly rounded to a hexadecimal floating number
with the given precision.
For a and A conversions, if FLT_RADIX is not a power of 2 and the
result is not exactly representable in the given precision, the result
should be one of the two adjacent numbers in hexadecimal floating style
with the given precision, with the extra stipulation that the error
should have a correct sign for the current rounding direction.
For the e, E, f, F, g, and G conversion specifiers, if the number of
significant decimal digits is at most DECIMAL_DIG, then the result
should be correctly rounded. If the number of significant decimal dig-
its is more than DECIMAL_DIG but the source value is exactly repre-
sentable with DECIMAL_DIG digits, then the result should be an exact
representation with trailing zeros. Otherwise, the source value is
bounded by two adjacent decimal strings L < U, both having DECIMAL_DIG
significant digits; the value of the resultant decimal string D should
satisfy L <= D <= U, with the extra stipulation that the error should
have a correct sign for the current rounding direction.
The last data modification and last file status change timestamps of
the file shall be marked for update:
1. Between the call to a successful execution of fprintf() or printf()
and the next successful completion of a call to fflush() or
fclose() on the same stream or a call to exit() or abort()
2. Upon successful completion of a call to dprintf()
RETURN VALUE
Upon successful completion, the dprintf(), fprintf(), and printf()
functions shall return the number of bytes transmitted.
Upon successful completion, the sprintf() function shall return the
number of bytes written to s, excluding the terminating null byte.
Upon successful completion, the snprintf() function shall return the
number of bytes that would be written to s had n been sufficiently
large excluding the terminating null byte.
If an output error was encountered, these functions shall return a neg-
ative value and set errno to indicate the error.
If the value of n is zero on a call to snprintf(), nothing shall be
written, the number of bytes that would have been written had n been
sufficiently large excluding the terminating null shall be returned,
and s may be a null pointer.
ERRORS
For the conditions under which dprintf(), fprintf(), and printf() fail
and may fail, refer to fputc() or fputwc().
In addition, all forms of fprintf() shall fail if:
EILSEQ A wide-character code that does not correspond to a valid char-
acter has been detected.
EOVERFLOW
The value to be returned is greater than {INT_MAX}.
In addition, all forms of fprintf() may fail if:
EINVAL There are insufficient arguments.
The dprintf() function may fail if:
EBADF The fildes argument is not a valid file descriptor.
The dprintf(), fprintf(), and printf() functions may fail if:
ENOMEM Insufficient storage space is available.
The snprintf() function shall fail if:
EOVERFLOW
The value of n is greater than {INT_MAX}.
The following sections are informative.
EXAMPLES
Printing Language-Independent Date and Time
The following statement can be used to print date and time using a lan-
guage-independent format:
printf(format, weekday, month, day, hour, min);
For American usage, format could be a pointer to the following string:
"%s, %s %d, %d:%.2d\n"
This example would produce the following message:
Sunday, July 3, 10:02
For German usage, format could be a pointer to the following string:
"%1$s, %3$d. %2$s, %4$d:%5$.2d\n"
This definition of format would produce the following message:
Sonntag, 3. Juli, 10:02
Printing File Information
The following example prints information about the type, permissions,
and number of links of a specific file in a directory.
The first two calls to printf() use data decoded from a previous stat()
call. The user-defined strperm() function shall return a string similar
to the one at the beginning of the output for the following command:
ls -l
The next call to printf() outputs the owner's name if it is found using
getpwuid(); the getpwuid() function shall return a passwd structure
from which the name of the user is extracted. If the user name is not
found, the program instead prints out the numeric value of the user ID.
The next call prints out the group name if it is found using get-
grgid(); getgrgid() is very similar to getpwuid() except that it shall
return group information based on the group number. Once again, if the
group is not found, the program prints the numeric value of the group
for the entry.
The final call to printf() prints the size of the file.
#include <stdio.h>
#include <sys/types.h>
#include <pwd.h>
#include <grp.h>
char *strperm (mode_t);
...
struct stat statbuf;
struct passwd *pwd;
struct group *grp;
...
printf("%10.10s", strperm (statbuf.st_mode));
printf("%4d", statbuf.st_nlink);
if ((pwd = getpwuid(statbuf.st_uid)) != NULL)
printf(" %-8.8s", pwd->pw_name);
else
printf(" %-8ld", (long) statbuf.st_uid);
if ((grp = getgrgid(statbuf.st_gid)) != NULL)
printf(" %-8.8s", grp->gr_name);
else
printf(" %-8ld", (long) statbuf.st_gid);
printf("%9jd", (intmax_t) statbuf.st_size);
...
Printing a Localized Date String
The following example gets a localized date string. The nl_langinfo()
function shall return the localized date string, which specifies the
order and layout of the date. The strftime() function takes this infor-
mation and, using the tm structure for values, places the date and time
information into datestring. The printf() function then outputs dat-
estring and the name of the entry.
#include <stdio.h>
#include <time.h>
#include <langinfo.h>
...
struct dirent *dp;
struct tm *tm;
char datestring[256];
...
strftime(datestring, sizeof(datestring), nl_langinfo (D_T_FMT), tm);
printf(" %s %s\n", datestring, dp->d_name);
...
Printing Error Information
The following example uses fprintf() to write error information to
standard error.
In the first group of calls, the program tries to open the password
lock file named LOCKFILE. If the file already exists, this is an
error, as indicated by the O_EXCL flag on the open() function. If the
call fails, the program assumes that someone else is updating the pass-
word file, and the program exits.
The next group of calls saves a new password file as the current pass-
word file by creating a link between LOCKFILE and the new password file
PASSWDFILE.
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#define LOCKFILE "/etc/ptmp"
#define PASSWDFILE "/etc/passwd"
...
int pfd;
...
if ((pfd = open(LOCKFILE, O_WRONLY | O_CREAT | O_EXCL,
S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)) == -1)
{
fprintf(stderr, "Cannot open /etc/ptmp. Try again later.\n");
exit(1);
}
...
if (link(LOCKFILE,PASSWDFILE) == -1) {
fprintf(stderr, "Link error: %s\n", strerror(errno));
exit(1);
}
...
Printing Usage Information
The following example checks to make sure the program has the necessary
arguments, and uses fprintf() to print usage information if the
expected number of arguments is not present.
#include <stdio.h>
#include <stdlib.h>
...
char *Options = "hdbtl";
...
if (argc < 2) {
fprintf(stderr, "Usage: %s -%s <file\n", argv[0], Options); exit(1);
}
...
Formatting a Decimal String
The following example prints a key and data pair on stdout. Note use
of the <asterisk> ('*') in the format string; this ensures the correct
number of decimal places for the element based on the number of ele-
ments requested.
#include <stdio.h>
...
long i;
char *keystr;
int elementlen, len;
...
while (len < elementlen) {
...
printf("%s Element%0*ld\n", keystr, elementlen, i);
...
}
Creating a Pathname
The following example creates a pathname using information from a pre-
vious getpwnam() function that returned the password database entry of
the user.
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
...
char *pathname;
struct passwd *pw;
size_t len;
...
// digits required for pid_t is number of bits times
// log2(10) = approx 10/33
len = strlen(pw->pw_dir) + 1 + 1+(sizeof(pid_t)*80+32)/33 +
sizeof ".out";
pathname = malloc(len);
if (pathname != NULL)
{
snprintf(pathname, len, "%s/%jd.out", pw->pw_dir,
(intmax_t)getpid());
...
}
Reporting an Event
The following example loops until an event has timed out. The pause()
function waits forever unless it receives a signal. The fprintf()
statement should never occur due to the possible return values of
pause().
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
...
while (!event_complete) {
...
if (pause() != -1 || errno != EINTR)
fprintf(stderr, "pause: unknown error: %s\n", strerror(errno));
}
...
Printing Monetary Information
The following example uses strfmon() to convert a number and store it
as a formatted monetary string named convbuf. If the first number is
printed, the program prints the format and the description; otherwise,
it just prints the number.
#include <monetary.h>
#include <stdio.h>
...
struct tblfmt {
char *format;
char *description;
};
struct tblfmt table[] = {
{ "%n", "default formatting" },
{ "%11n", "right align within an 11 character field" },
{ "%#5n", "aligned columns for values up to 99999" },
{ "%=*#5n", "specify a fill character" },
{ "%=0#5n", "fill characters do not use grouping" },
{ "%^#5n", "disable the grouping separator" },
{ "%^#5.0n", "round off to whole units" },
{ "%^#5.4n", "increase the precision" },
{ "%(#5n", "use an alternative pos/neg style" },
{ "%!(#5n", "disable the currency symbol" },
};
...
float input[3];
int i, j;
char convbuf[100];
...
strfmon(convbuf, sizeof(convbuf), table[i].format, input[j]);
if (j == 0) {
printf("%s%s%s\n", table[i].format,
convbuf, table[i].description);
}
else {
printf("%s\n", convbuf);
}
...
Printing Wide Characters
The following example prints a series of wide characters. Suppose that
"L`@`" expands to three bytes:
wchar_t wz [3] = L"@@"; // Zero-terminated
wchar_t wn [3] = L"@@@"; // Unterminated
fprintf (stdout,"%ls", wz); // Outputs 6 bytes
fprintf (stdout,"%ls", wn); // Undefined because wn has no terminator
fprintf (stdout,"%4ls", wz); // Outputs 3 bytes
fprintf (stdout,"%4ls", wn); // Outputs 3 bytes; no terminator needed
fprintf (stdout,"%9ls", wz); // Outputs 6 bytes
fprintf (stdout,"%9ls", wn); // Outputs 9 bytes; no terminator needed
fprintf (stdout,"%10ls", wz); // Outputs 6 bytes
fprintf (stdout,"%10ls", wn); // Undefined because wn has no terminator
In the last line of the example, after processing three characters,
nine bytes have been output. The fourth character must then be examined
to determine whether it converts to one byte or more. If it converts to
more than one byte, the output is only nine bytes. Since there is no
fourth character in the array, the behavior is undefined.
APPLICATION USAGE
If the application calling fprintf() has any objects of type wint_t or
wchar_t, it must also include the <wchar.h> header to have these
objects defined.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
Section 2.5, Standard I/O Streams, fputc(), fscanf(), setlocale(),
strfmon(), wcrtomb()
The Base Definitions volume of POSIX.1-2008, Chapter 7, Locale,
<stdio.h>, <wchar.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker-
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 FPRINTF(3P)
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