man3/asprintf.3

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  27 .TH ASPRINTF 3 2019-03-06 "GNU" "Linux Programmer's Manual"
  28 .SH NAME
  29 asprintf, vasprintf \- print to allocated string
  30 .SH SYNOPSIS
  31 .BR "#define _GNU_SOURCE" "         /* See feature_test_macros(7) */"
  32 .br
  33 .B #include <stdio.h>
  34 .PP
  35 .BI "int asprintf(char **" strp ", const char *" fmt ", ...);"
  36 .PP
  37 .BI "int vasprintf(char **" strp ", const char *" fmt ", va_list " ap );
  38 .SH DESCRIPTION
  39 The functions
  40 .BR asprintf ()
  41 and
  42 .BR vasprintf ()
  43 are analogs of
  44 .BR sprintf (3)
  45 and
  46 .BR vsprintf (3),
  47 except that they allocate a string large enough to hold the output
  48 including the terminating null byte (\(aq\e0\(aq),
  49 and return a pointer to it via the first argument.
  50 This pointer should be passed to
  51 .BR free (3)
  52 to release the allocated storage when it is no longer needed.
  53 .SH RETURN VALUE
  54 When successful, these functions return the number of bytes printed,
  55 just like
  56 .BR sprintf (3).
  57 If memory allocation wasn't possible, or some other error occurs,
  58 these functions will return \-1, and the contents of
  59 .I strp
  60 are undefined.
  61 .SH ATTRIBUTES
  62 For an explanation of the terms used in this section, see
  63 .BR attributes (7).
  64 .TS
  65 allbox;
  66 lbw23 lb lb
  67 l l l.
  68 Interface       Attribute       Value
  69 T{
  70 .BR asprintf (),
  71 .BR vasprintf ()
  72 T}      Thread safety   MT-Safe locale
  73 .TE
  74 .sp 1
  75 .SH CONFORMING TO
  76 These functions are GNU extensions, not in C or POSIX.
  77 They are also available under *BSD.
  78 The FreeBSD implementation sets
  79 .I strp
  80 to NULL on error.
  81 .SH SEE ALSO
  82 .BR free (3),
  83 .BR malloc (3),
  84 .BR printf (3)