asprintf(3) Library Functions Manual asprintf(3)
NAME
asprintf, vasprintf - print to allocated string
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <stdio.h>
int asprintf(char **restrict strp, const char *restrict fmt, ...);
int vasprintf(char **restrict strp, const char *restrict fmt,
va_list ap);
DESCRIPTION
The functions asprintf() and vasprintf() are analogs of sprintf(3) and
vsprintf(3), except that they allocate a string large enough to hold
the output including the terminating null byte ('\0'), and return a
pointer to it via the first argument. This pointer should be passed to
free(3) to release the allocated storage when it is no longer needed.
RETURN VALUE
When successful, these functions return the number of bytes printed,
just like sprintf(3). If memory allocation wasn't possible, or some
other error occurs, these functions will return -1, and the contents of
strp are undefined.
ATTRIBUTES
For an explanation of the terms used in this section, see attrib-
utes(7).
┌────────────────────────────────────┬───────────────┬────────────────┐
│ Interface │ Attribute │ Value │
├────────────────────────────────────┼───────────────┼────────────────┤
│ asprintf(), vasprintf() │ Thread safety │ MT-Safe locale │
└────────────────────────────────────┴───────────────┴────────────────┘
VERSIONS
The FreeBSD implementation sets strp to NULL on error.
STANDARDS
GNU, BSD.
SEE ALSO
free(3), malloc(3), printf(3)
Linux man-pages 6.7 2023-10-31 asprintf(3)
Generated by dwww version 1.16 on Tue Dec 16 11:09:00 CET 2025.