ASPRINTF(3) Linux Programmer's Manual ASPRINTF(3)
asprintf, vasprintf - print to allocated string
#define _GNU_SOURCE /* See feature_test_macros(7) */
int asprintf(char **strp, const char *fmt, ...);
int vasprintf(char **strp, const char *fmt, va_list ap);
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.
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 is undefined.
These functions are GNU extensions, not in C or POSIX. They are also available under
*BSD. The FreeBSD implementation sets strp to NULL on error.
free(3), malloc(3), printf(3)
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GNU 2013-06-21 ASPRINTF(3)