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FPRINTF(3P) POSIX Programmer's Manual FPRINTF(3P)
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.
dprintf, fprintf, printf, snprintf, sprintf — print formatted
output
#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, ...);
Excluding dprintf(): The functionality described on this
reference page is aligned with the ISO C standard. Any conflict
between the requirements described here and the ISO C standard is
unintentional. This volume of POSIX.1‐2017 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, beginning and ending in its initial shift state, if any.
The format is composed 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 format. 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$", where n is a decimal integer in
the range [1,{NL_ARGMAX}], giving the position of the argument in
the argument list. This feature provides for the definition of
format strings that select arguments in an order appropriate to
specific languages (see the EXAMPLES section).
The format can contain either numbered argument conversion
specifications (that is, "%n$" 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$" form of conversion
specification, numbered arguments in the argument list can be
referenced from the format string as many times as required.
In format strings containing the % form of conversion
specification, each conversion specification uses the first
unused argument in the argument list.
All forms of the fprintf() functions allow for the insertion of a
language-dependent radix character in the output string. The
radix character is defined in the current locale (category
LC_NUMERIC). In the POSIX locale, or in a locale where the radix
character is not defined, the radix character shall default to a
<period> ('.').
Each conversion specification is introduced by the '%' character
or by the character sequence "%n$", 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> characters 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 number of digits to appear after the radix character for
the a, A, e, E, f, and F conversion specifiers; the maximum
number of significant 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 conversion 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 specifier,
the behavior is undefined.
* An optional length modifier that specifies the size of the
argument.
* A conversion specifier character that indicates the type of
conversion 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 conversions 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 specified.
<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 shall increase the
precision, if and only if necessary, to force the first
digit of the result to be a zero (if the value and
precision are both 0, a single 0 is printed). 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 conversions only if a digit
follows it. For g and G conversion specifiers, trailing
zeros shall not be removed from the result as they
normally are. For other conversion specifiers, the
behavior 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 behavior is undefined.
The length modifiers and their meanings are:
hh Specifies that a following d, i, o, u, x, or X conversion
specifier applies to a signed char or unsigned char
argument (the argument will have been promoted according
to the integer promotions, but its value shall be
converted to signed char or unsigned char before
printing); or that a following n conversion specifier
applies to a pointer to a signed char argument.
h Specifies that a following d, i, o, u, x, or X conversion
specifier applies to a short or unsigned short argument
(the argument will have been promoted according to the
integer promotions, but its value shall be converted to
short or unsigned short before printing); or that a
following n conversion specifier applies to a pointer to
a short argument.
l (ell) Specifies that a following d, i, o, u, x, or X conversion
specifier applies to a long or unsigned long argument;
that a following 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
specifier 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
specifier 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
specifier 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
specifier 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 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.
o The unsigned argument shall be 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
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
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 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 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 character 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 implementation-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 converted 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 converted 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 fractional portion remaining.
A double argument representing an infinity or NaN shall
be converted 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 hexadecimal 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 decimal-point character
shall appear. The letters "abcdef" shall be used for a
conversion and the letters "ABCDEF" for A conversion. 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 converted 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 element 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 application 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. Characters 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 digits is more than DECIMAL_DIG but the source value is
exactly representable 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()
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 negative 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.
For the conditions under which dprintf(), fprintf(), and printf()
fail and may fail, refer to fputc(3p) or fputwc(3p).
In addition, all forms of fprintf() shall fail if:
EILSEQ A wide-character code that does not correspond to a valid
character has been detected.
EOVERFLOW
The value to be returned is greater than {INT_MAX}.
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.
Printing Language-Independent Date and Time
The following statement can be used to print date and time using
a language-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
getgrgid(); 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 information and, using the tm structure for
values, places the date and time information into datestring.
The printf() function then outputs datestring 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 password file, and the program exits.
The next group of calls saves a new password file as the current
password 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 elements 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
previous 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.
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.
If an implementation detects that there are insufficient
arguments for the format, it is recommended that the function
should fail and report an [EINVAL] error.
None.
Section 2.5, Standard I/O Streams, fputc(3p), fscanf(3p),
setlocale(3p), strfmon(3p), wcrtomb(3p)
The Base Definitions volume of POSIX.1‐2017, Chapter 7, Locale,
inttypes.h(0p), stdio.h(0p), wchar.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. 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.opengroup.org/unix/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.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 FPRINTF(3P)
Pages that refer to this page: stdarg.h(0p), stdio.h(0p), date(1p), printf(1p), closelog(3p), dprintf(3p), fmtmsg(3p), fscanf(3p), fwrite(3p), localeconv(3p), perror(3p), printf(3p), setlocale(3p), snprintf(3p), sprintf(3p), stdin(3p), strfmon(3p), strptime(3p), vfprintf(3p)
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