defer.cpp

#include <iostream>
#include <functional>
#include <memory>

#define GET_RETURN_VALUE64(VAR)               \
       asm ("nop\n nop\n movq %%rax,%0 \n nop\n"       \
             : "=r" (VAR)                     \
             : \
             : "rax" \
           );
#define GET_RETURN_VALUE32(VAR)               \
       asm ("movl %0,%%rax"                  \
             : "=r" (VAR)                    \
            );


#define CONCAT1(X,Y) X##Y 
#define CONCAT(X,Y) CONCAT1(X,Y)
#define DEFER(BODY) \
  std::unique_ptr<int, std::function<void(int*)>>     \
   CONCAT(_defer,__LINE__)(reinterpret_cast<int*>(1), \
     [&](int*) BODY );


int foo () {
    
    int x = 31;
    std::cout << "Hello From Foo." << std::endl;
    DEFER({
        int64_t returned_code = 0;
        GET_RETURN_VALUE64(returned_code);
        std::cout << "\tDefer foo x = " << x
          << " returned " << returned_code << std::endl;
    });
    
    std::cout << "Foo is returning..." << std::endl;
    return 1234;
}

int main ( void ) {
    int ret = foo();
    std::cout << "foo() = " << ret;
    return 55;
}