Question

I have problem and no idea how to resolve it. I believe this is stupid trivial:

I have 3 files:
Util.hpp

class Util  
{  
    public:  
        class BitParser  
        {
            public:
                static bool getBitAt(int buf, int idx);  
        };  
};  

Util.cpp

#include "Util.hpp"
bool Util::BitParser::getBitAt(int buf, int idx)
{
    return true;
}

application.cpp

#include "Util.hpp"
int main(int argc, char* argv[])
{
    Util::BitParser::getBitAt(1,1);
}

Of couse, files listed above are in the same directory. And now when I try to link and compile I recieve linker error:

$ g++ -o app application.cpp
application.cpp:(.text+0x19): undefined reference to `Util::BitParser::getBitAt(int, int)'
collect2: ld returned 1 exit status

What is screwed up?

Answer 1

You told g++ to compile your ‘main’ program, but didn’t tell it about the Util module. Add Util.cpp to the command line and all should work well.

The compiler has brewn an “application.o” file that refers to the Util::bitparser functions.

The linker should ‘link’ these referrals to the “util.o” file, containing the actual code for these functions. But it has no .o file containing a function satisfying the link. That’s what it calls “undefined reference”: “application.o” refers to a function the linker doesn’t find.