.\" 2000-07-26 jsm28@hermes.cam.ac.uk - three small fixes
.\" 2000-10-16 jsm28@hermes.cam.ac.uk - more fixes
.\"
-.TH PRINTF 3 2015-04-19 "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,
+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 ():
.RS 4
-_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500 || _ISOC99_SOURCE ||
-_POSIX_C_SOURCE\ >=\ 200112L;
-.br
-or
-.I "cc -std=c99"
+_XOPEN_SOURCE\ >=\ 500 || _ISOC99_SOURCE ||
+ || /* Glibc versions <= 2.19: */ _BSD_SOURCE
.RE
-.sp
+.PP
.BR dprintf (),
.BR vdprintf ():
.PD 0
.RS 4
.TP 4
Since glibc 2.10:
-_XOPEN_SOURCE\ >=\ 700 || _POSIX_C_SOURCE\ >=\ 200809L
+_POSIX_C_SOURCE\ >=\ 200809L
.TP
Before glibc 2.10:
_GNU_SOURCE
.BR vsnprintf ()
write to the character string
.IR str .
-
+.PP
The function
.BR dprintf ()
is the same as
-.BR fprintf (3)
+.BR fprintf ()
except that it outputs to a file descriptor,
.IR fd ,
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 (),
(e.g., if the target string array and one of the supplied input arguments
refer to the same buffer).
See NOTES.
-.SS Return value
-Upon successful return, these functions return the number of characters
-printed (excluding the null byte used to end output to strings).
-
-The functions
-.BR snprintf ()
-and
-.BR vsnprintf ()
-do not write more than
-.I size
-bytes (including the terminating null byte (\(aq\e0\(aq)).
-If the output was truncated due to this limit, then the return value
-is the number of characters (excluding the terminating null byte)
-which would have been written to the final string if enough space
-had been available.
-Thus, a return value of
-.I size
-or more means that the output was truncated.
-(See also below under NOTES.)
-
-If an output error is encountered, a negative value is returned.
.SS Format of the format string
The format string is a character string, beginning and ending
in its initial shift state, if any.
.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
-given, where each \(aq*\(aq and each conversion specifier asks for the next
+given, where each \(aq*\(aq (see
+.I "Field width"
+and
+.I Precision
+below) and each conversion specifier asks for the next
argument (and it is an error if insufficiently many arguments are given).
One can also specify explicitly which argument is taken,
at each place where an argument is required, by writing "%m$" instead
of \(aq%\(aq and "*m$" instead of \(aq*\(aq,
-where the decimal integer m denotes
+where the decimal integer \fIm\fP denotes
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.
If the style using
\(aq$\(aq is used, it must be used throughout for all conversions taking an
argument and all width and precision arguments, but it may be mixed
-with "%%" formats which do not consume an argument.
+with "%%" formats, which do not consume an argument.
There may be no
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 The flag characters
+.SS Flag characters
The character % is followed by zero or more of the following flags:
.TP
.B #
.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.
For example, since glibc 2.2.3 this will give Arabic-Indic digits
in the Persian ("fa_IR") locale.
.\" outdigits keyword in locale file
-.SS The field width
+.SS Field width
An optional decimal digit string (with nonzero first digit) specifying
a minimum field width.
If the converted value has fewer characters
In no case does 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 is expanded to contain the conversion result.
-.SS The precision
+.SS Precision
An optional precision, in the form of a period (\(aq.\(aq) followed by an
optional decimal digit string.
Instead of a decimal digit string one may write "*" or "*m$"
-(for some decimal integer m) to specify that the precision
-is given in the next argument, or in the m-th argument, respectively,
+(for some decimal integer \fIm\fP) to specify that the precision
+is given in the next argument, or in the \fIm\fP-th argument, respectively,
which must be of type
.IR int .
If the precision is given as just \(aq.\(aq, the precision is taken to
and
.B S
conversions.
-.SS The length modifier
+.SS Length modifier
Here, "integer conversion" stands for
.BR d ,
.BR i ,
.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 ).
-.SS The conversion specifier
+.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:
.TP
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
The C99 standard specifies "[\-]inf" or "[\-]infinity"
for infinity, and a string starting with "nan" for NaN, in the case of
.B f
-conversion, and "[\-]INF" or "[\-]INFINITY" or "NAN*" in the case of
+conversion, and "[\-]INF" or "[\-]INFINITY" or "NAN" in the case of
.B F
conversion.)
.TP
.B s
If no
.B l
-modifier is present: The
+modifier is present: the
.I "const char\ *"
argument is expected to be a pointer to an array of character type (pointer
to a string).
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
+modifier is present: the
.I "const wchar_t\ *"
argument is expected to be a pointer to an array of wide characters.
Wide characters from the array are converted to multibyte characters
or variant whose size matches the (optionally)
supplied integer length modifier.
No argument is converted.
+(This specifier is not supported by the bionic C library.)
The behavior is undefined if the conversion specification includes
any flags, a field width, or a precision.
.TP
.B m
-(Glibc extension.)
+(Glibc extension; supported by uClibc and musl.)
Print output of
.IR strerror(errno) .
No argument is required.
No argument is converted.
The complete conversion
specification is \(aq%%\(aq.
+.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
+.BR vsnprintf ()
+do not write more than
+.I size
+bytes (including the terminating null byte (\(aq\e0\(aq)).
+If the output was truncated due to this limit, then the return value
+is the number of characters (excluding the terminating null byte)
+which would have been written to the final string if enough space
+had been available.
+Thus, a return value of
+.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 attributes (7).
.BR vsnprintf ()
T} Thread safety MT-Safe locale
.TE
-
+.sp 1
.SH CONFORMING TO
-The
.BR fprintf (),
.BR printf (),
.BR sprintf (),
.BR vprintf (),
.BR vfprintf (),
-and
-.BR vsprintf ()
-functions conform to C89 and C99.
-
-The
-.BR snprintf ()
-and
-.BR vsnprintf ()
-functions conform to C99.
-
+.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
to be NULL in this case, and gives the return value (as always)
as the number of characters that would have been written in case
the output string has been large enough.
-SUSv3 and later align their specification of
+POSIX.1-2001 and later align their specification of
.BR snprintf ()
with C99.
.\" .PP
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>
if (size < 0)
return NULL;
- size++; /* For '\\0' */
+ size++; /* For '\\0' */
p = malloc(size);
if (p == NULL)
return NULL;
va_start(ap, fmt);
size = vsnprintf(p, size, fmt, ap);
+ va_end(ap);
+
if (size < 0) {
- free(p);
- return NULL;
+ 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.
.SH SEE ALSO
.BR printf (1),
.BR asprintf (3),
-.BR dprintf (3),
+.BR puts (3),
.BR scanf (3),
.BR setlocale (3),
+.BR strfromd (3),
.BR wcrtomb (3),
.BR wprintf (3),
.BR locale (5)
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