The functions asprintf and vasprintf are analogues of
sprintf and vsprintf, except that they allocate a string large
enough to hold the output including the terminating NUL, and return a pointer
to it via the first parameter. 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