C++ “undefined reference to“ in main method

Question

It looks basic and it’s probably due to a beginner mistake but I can’t figure out why...

When compiling I get an error like below from int main(): “undefined reference to 'Hello::World::PaintService::PaintService()"

paint.cpp

using namespace Hello;
int main(int argc, char **argv) {
    World::PaintService service;
     service.start_painting(argc[1]);

}

PaintService and start_painting are defined like below:

paint_service.h

namespace Hello {
namespace World {
    class PaintService {
        public:
            PaintService();
            void start_painting(...);
}; } }

paint_service.cpp

namespace Hello { 
namespace World {
    void start_painting(....) {
        ... //paint
    }
} }

It seems simple to call that start method like service.start_paint() in another class after calling PaintService service, but something is wrong. I have tried lots of variations yet couldn’t figure out :-/ Could someone point out what I’m doing wrong?

Thanks!

Is there an `#include "paint_service.h"` in your `paint.cpp` and `paint_service.cpp` that you didn't mention? — Nathan Pierson, Oct 14 '20 at 04:16
Relevant answer: https://stackoverflow.com/a/12574407/962089. It's possible [this answer](https://stackoverflow.com/questions/12573816/what-is-an-undefined-reference-unresolved-external-symbol-error-and-how-do-i-fix/12574403#12574403) is relevant for your constructor too. — chris, Oct 14 '20 at 04:19
@nathan pierson yes both of them have that paint_service.h as a header. — user2465084, Oct 14 '20 at 04:21

score 1 · Accepted Answer · answered Oct 14 '20 at 04:16

1

To declare a method, you need to include the name of the class.

namespace Hello {
namespace World {

void PaintService::start_painting(....) { ... }
void PaintService::PaintService() { ... }

}  // namespace World
}  // namespace Hello

https://repl.it/repls/PunySaneSpools#main.cpp

answered Oct 14 '20 at 04:16

Bill Lynch

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Thank you so much!!! This did it!!! But for some reason I had to take out the constructor (PaintService();) from both header file and cpp file... – user2465084 Oct 14 '20 at 04:39

C++ “undefined reference to“ in main method

1 Answers1