int vasprintf(char **strp, const char *fmt, va_list ap);
are analogs of
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
to release the allocated storage when it is no longer needed.
When successful, these functions return the number of bytes printed,
If memory allocation wasn't possible, or some other error occurs,
these functions will return -1, and the contents of
These functions are GNU extensions, not in C or POSIX.
They are also available under *BSD.
The FreeBSD implementation sets
to NULL on error.