generic way to print out variable name in c++

Question

given a class

struct {
  int a1;
  bool a2;
  ...
  char* a500;
  ...
  char a10000;      
}

I want to print or stream out

Answer 1

You can employ an evil macro:

#define DUMP(a) \
    do { std::cout << #a " is value " << (a) << std::endl; } while(false)

Usage example (Edit now updated with example for struct members):

#include 

#define DUMPSTR_WNAME(os, name, a) \
    do { (os) << (name) << " is value " << (a) << std::endl; } while(false)

#define DUMPSTR(os, a) DUMPSTR_WNAME((os), #a, (a))
#define DUMP(a)        DUMPSTR_WNAME(std::cout, #a, (a))

struct S {
    int a1;
    float a2;
    std::string a3;

    std::ostream& dump(std::ostream& os)
    {
        DUMPSTR(os, a1);
        DUMPSTR(os, a2);
        DUMPSTR(os, a3);
        return os;
    }
};

int main()
{
    S s = { 3, 3.14, "  03.1415926" };

    s.dump(std::cout);

    DUMP(s.a1);
    DUMP(s.a2);
    DUMP(s.a3);

    return 0;
}

See live demo on CodePad

Why the funny macro?

Answering the unasked question. Consider what happens if you nest the macro invocation in a conditional, or a for loop. Marshall Cline explains the rest