generic way to print out variable name in c++

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 <iostream>

#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

The feature you're looking for is typically called reflection. It is not part of C++, since in compiled languages the information you're after (human-readable variable names) is generally not kept by the compiler. It is not needed to run the code, so there's no point in including it.

Debuggers can often inspect either out-of-band symbol information, or symbol data kept in binaries for this very purpose, to show such names but re-doing that for this purpose is probably more work than it's worth.

I would suggest looking for some of the many "tricks" (=solutions) to implement this yourself.