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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, 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
free(3), malloc(3), printf(3)
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description of the project, and information about reporting bugs, can
be found at http://man7.org/linux/man-pages/.