re_string_get_buffer
char *buf = (char *) re_string_get_buffer (&mctx->input);
const char *buf = (const char *) re_string_get_buffer (&mctx->input);
buf = (const char *) re_string_get_buffer (&mctx->input);
buf = (const char *) re_string_get_buffer (&mctx->input);
buf = (const char *) re_string_get_buffer (&mctx->input);
= ((const unsigned char *) re_string_get_buffer (input) + str_idx);