.\" 2000-07-26 jsm28@hermes.cam.ac.uk - three small fixes
.\" 2000-10-16 jsm28@hermes.cam.ac.uk - more fixes
.\"
-.TH PRINTF 3 2016-12-12 "GNU" "Linux Programmer's Manual"
+.TH PRINTF 3 2017-09-15 "GNU" "Linux Programmer's Manual"
.SH NAME
printf, fprintf, dprintf, sprintf, snprintf, vprintf, vfprintf, vdprintf,
vsprintf, vsnprintf \- formatted output conversion
.SH SYNOPSIS
+.nf
.B #include <stdio.h>
-.sp
+.PP
.BI "int printf(const char *" format ", ...);"
-.br
.BI "int fprintf(FILE *" stream ", const char *" format ", ...);"
-.br
.BI "int dprintf(int " fd ", const char *" format ", ...);"
-.br
.BI "int sprintf(char *" str ", const char *" format ", ...);"
-.br
.BI "int snprintf(char *" str ", size_t " size ", const char *" format ", ...);"
-.sp
+
.B #include <stdarg.h>
-.sp
+.PP
.BI "int vprintf(const char *" format ", va_list " ap );
-.br
.BI "int vfprintf(FILE *" stream ", const char *" format ", va_list " ap );
-.br
.BI "int vdprintf(int " fd ", const char *" format ", va_list " ap );
-.br
.BI "int vsprintf(char *" str ", const char *" format ", va_list " ap );
-.br
.BI "int vsnprintf(char *" str ", size_t " size ", const char *" format \
", va_list " ap );
-.sp
+.fi
+.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
-.sp
+.PP
.ad l
.BR snprintf (),
.BR vsnprintf ():
_XOPEN_SOURCE\ >=\ 500 || _ISOC99_SOURCE ||
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE
.RE
-.sp
+.PP
.BR dprintf (),
.BR vdprintf ():
.PD 0
.BR vsnprintf ()
write to the character string
.IR str .
-
+.PP
The function
.BR dprintf ()
is the same as
instead of to a
.I stdio
stream.
-
+.PP
The functions
.BR snprintf ()
and
.I size
bytes (including the terminating null byte (\(aq\e0\(aq)) to
.IR str .
-
+.PP
The functions
.BR vprintf (),
.BR vfprintf (),
is undefined after the call.
See
.BR stdarg (3).
-
+.PP
All of these functions write the output under the control of a
.I format
string that specifies how subsequent arguments (or arguments accessed via
the variable-length argument facilities of
.BR stdarg (3))
are converted for output.
-
+.PP
C99 and POSIX.1-2001 specify that the results are undefined if a call to
.BR sprintf (),
.BR snprintf (),
.I precision
and an optional
.IR "length modifier" .
-
+.PP
The arguments must correspond properly (after type promotion) with the
conversion specifier.
By default, the arguments are used in the order
the position in the argument list of the desired argument, indexed starting
from 1.
Thus,
+.PP
.in +4n
-.nf
-
+.EX
printf("%*d", width, num);
-
-.fi
+.EE
.in
+.PP
and
+.PP
.in +4n
-.nf
-
+.EX
printf("%2$*1$d", width, num);
-
-.fi
+.EE
.in
+.PP
are equivalent.
The second style allows repeated references to the
same argument.
gaps in the numbers of arguments specified using \(aq$\(aq; for example, if
arguments 1 and 3 are specified, argument 2 must also be specified
somewhere in the format string.
-
+.PP
For some numeric conversions a radix character ("decimal point") or
thousands' grouping character is used.
The actual character used
depends on the
.B LC_NUMERIC
part of the locale.
+(See
+.BR setlocale (3).)
The POSIX locale
uses \(aq.\(aq as radix character, and does not have a grouping character.
Thus,
+.PP
.in +4n
-.nf
-
+.EX
printf("%\(aq.2f", 1234567.89);
-
-.fi
+.EE
.in
+.PP
results in "1234567.89" in the POSIX locale, in "1234567,89" in the
nl_NL locale, and in "1.234.567,89" in the da_DK locale.
.SS Flag characters
.BR G )
the output is to be grouped with thousands' grouping characters
if the locale information indicates any.
+(See
+.BR setlocale (3).)
Note that many versions of
.BR gcc (1)
cannot parse this option and will issue a warning.
.I long long int
argument.
.TP
+.B q
+A synonym for
+.BR ll .
+This is a nonstandard extension, derived from BSD;
+avoid its use in new code.
+.TP
.B L
A following
.BR a ,
.I long double
argument.
(C99 allows %LF, but SUSv2 does not.)
-.\" .TP
-.\" .B q
-.\" ("quad". 4.4BSD and Linux libc5 only.
-.\" Don't use.)
-This is a synonym for
-.BR ll .
.TP
.B j
A following integer conversion corresponds to an
conversion corresponds to a pointer to a
.I size_t
argument.
-.\" (Linux libc5 has
-.\" .B Z
-.\" with this meaning.
-.\" Don't use it.)
+.TP
+.B Z
+A nonstandard synonym for
+.BR z
+that predates the appearance of
+.BR z .
+Do not use in new code.
.TP
.B t
A following integer conversion corresponds to a
.I ptrdiff_t
argument.
.PP
-SUSv3 specifies all of the above.
+SUSv3 specifies all of the above,
+except for those modifiers explicitly noted as being nonstandard extensions.
SUSv2 specified only the length modifiers
.B h
(in
.BR Lf ,
.BR Lg ,
.BR LG ).
+.PP
+As a nonstandard extension, the GNU implementations treats
+.B ll
+and
+.B L
+as synonyms, so that one can, for example, write
+.BR llg
+(as a synonym for the standards-compliant
+.RB Lg )
+and
+.BR Ld
+(as a synonym for the standards compliant
+.BR lld ).
+Such usage is nonportable.
+.\"
.SS Conversion specifiers
A character that specifies the type of conversion to be applied.
The conversion specifiers and their meanings are:
If the precision is missing, it is taken as
6; if the precision is explicitly zero, no decimal-point character appears.
If a decimal point appears, at least one digit appears before it.
-
+.IP
(SUSv2 does not know about
.B F
and says that character string representations for infinity and NaN
If a precision is given, no null byte need be present;
if the precision is not specified, or is greater than the size of the
array, the array must contain a terminating null byte.
-
+.IP
If an
.B l
modifier is present: the
.SH RETURN VALUE
Upon successful return, these functions return the number of characters
printed (excluding the null byte used to end output to strings).
-
+.PP
The functions
.BR snprintf ()
and
.I size
or more means that the output was truncated.
(See also below under NOTES.)
-
+.PP
If an output error is encountered, a negative value is returned.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR vsnprintf ()
T} Thread safety MT-Safe locale
.TE
-
+.sp 1
.SH CONFORMING TO
.BR fprintf (),
.BR printf (),
.BR vfprintf (),
.BR vsprintf ():
POSIX.1-2001, POSIX.1-2008, C89, C99.
-
+.PP
.BR snprintf (),
.BR vsnprintf ():
POSIX.1-2001, POSIX.1-2008, C99.
-
+.PP
The
.BR dprintf ()
and
and the flag character \fBI\fP.
.SH NOTES
Some programs imprudently rely on code such as the following
-
+.PP
sprintf(buf, "%s some further text", buf);
-
+.PP
to append text to
.IR buf .
However, the standards explicitly note that the results are undefined
used, and the compiler options employed, calls such as the above will
.B not
produce the expected results.
-
+.PP
The glibc implementation of the functions
.BR snprintf ()
and
To print
.I Pi
to five decimal places:
+.PP
.in +4n
-.nf
-
+.EX
#include <math.h>
#include <stdio.h>
fprintf(stdout, "pi = %.5f\en", 4 * atan(1.0));
-.fi
+.EE
.in
.PP
To print a date and time in the form "Sunday, July 3, 10:02",
and
.I month
are pointers to strings:
+.PP
.in +4n
-.nf
-
+.EX
#include <stdio.h>
fprintf(stdout, "%s, %s %d, %.2d:%.2d\en",
weekday, month, day, hour, min);
-.fi
+.EE
.in
.PP
Many countries use the day-month-year order.
Hence, an internationalized version must be able to print
the arguments in an order specified by the format:
+.PP
.in +4n
-.nf
-
+.EX
#include <stdio.h>
fprintf(stdout, format,
weekday, month, day, hour, min);
-
-.fi
+.EE
.in
+.PP
where
.I format
depends on locale, and may permute the arguments.
With the value:
+.PP
.in +4n
-.nf
-
+.EX
"%1$s, %3$d. %2$s, %4$d:%5$.2d\en"
-
-.fi
+.EE
.in
+.PP
one might obtain "Sonntag, 3. Juli, 10:02".
.PP
To allocate a sufficiently large string and print into it
(code correct for both glibc 2.0 and glibc 2.1):
-.nf
-
+.PP
+.EX
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
va_start(ap, fmt);
size = vsnprintf(p, size, fmt, ap);
+ va_end(ap);
+
if (size < 0) {
free(p);
return NULL;
}
- va_end(ap);
return p;
}
-.fi
+.EE
.PP
If truncation occurs in glibc versions prior to 2.0.6, this is treated as an
error instead of being handled gracefully.
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