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'\" t
.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH asprintf 3 2025-05-21 "Linux man-pages (unreleased)"
.SH NAME
asprintf, vasprintf \- print to allocated string
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */"
.B #include <stdio.h>
.P
.BI "int asprintf(char **restrict " strp ", const char *restrict " fmt ", ...);"
.BI "int vasprintf(char **restrict " strp ", const char *restrict " fmt ,
.BI " va_list " ap );
.fi
.SH DESCRIPTION
The functions
.BR asprintf ()
and
.BR vasprintf ()
are analogs of
.BR sprintf (3)
and
.BR vsprintf (3),
except that they allocate a string large enough to hold the output
including the terminating null byte (\[aq]\[rs]0\[aq]),
and return a pointer to it via the first argument.
This pointer should be passed to
.BR free (3)
to release the allocated storage when it is no longer needed.
.SH RETURN VALUE
When successful, these functions return the number of bytes printed,
just like
.BR sprintf (3).
On error,
\-1 is returned,
.I errno
is set to indicate the error,
and the contents of
.I strp
are undefined.
.SH ERRORS
See
.BR sprintf (3)
and
.BR malloc (3).
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface Attribute Value
T{
.na
.nh
.BR asprintf (),
.BR vasprintf ()
T} Thread safety MT-Safe locale
.TE
.SH VERSIONS
The FreeBSD implementation sets
.I strp
to NULL on error.
.SH STANDARDS
GNU, BSD.
.SH SEE ALSO
.BR free (3),
.BR malloc (3),
.BR printf (3)
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