Question

struct s1 { int a; int b; };
struct s2 { int a; int b; };

struct s2 test(void) {
    struct s1 s = { 1, 2 };
    return s; // incompatible types
}

In the above code, can I return s without creating a new struct s2 variable and populating it with s‘s values? It is guaranteed that struct s1 will always be identical to struct s2.

Answer 1

You can’t return the struct directly, but you can avoid
creating a separate variable in your source code by using a compound literal,
which is a feature of C99.

struct s2 test(void) {
  struct s1 s = { 1, 2 };
  return (struct s2){s.a, s.b};
}