比较

#include "apue.h"typedef  void Mytype(int a, int b);void foo(int a, int b){    printf("a+b=%d\n",a+b);}int main(int argc,char * argv[]){  Mytype * ptr_foo;  Mytype foo;  void (*f3)();  ptr_foo=foo;  f3=foo;  ptr_foo(1,2);  f3(1,2);  foo(1,2);  return 0;}