string concat with asprintf

asprintf.c

std::string foo_string = "foo";
std::string bar_string = "bar";
std::string res;
char * tmp;
if (asprintf(&tmp, "concatenation: %s %s", foo_string.c_str(), bar_string.c_str()) != -1) {
  res = tmp;
  free(tmp);
} else {
  throw Exception("Out of memory");
}