CODEWITHSUNDEEP
c++g++
daenin
daenin

Reputation: 31

"Undefined symbols for architecture x86_64" - once again (tiny example)

I am stuck with the apparently common yet very cryptic compilation error

Undefined symbols for architecture x86_64:
  "_main", referenced from:
     implicit entry/start for main executable
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

I narrowed it down to a tiny implementation (from a tutorial) which just won't compile.

Header file: Num.h

class Num
{
 private:
 int num;
 public:
 Num(int n);
 int getNum();
};

Implementation: Num.cpp

#include "Num.h"
Num::Num(int n): num(n) {}
int Num::getNum()
{
 return num;
}

Compilation command:

g++  Num.cpp

I don't see any obvious hints in the invocation stack (via g++ Num.cpp -v ).

Both Num.h and Num.cpp are located in the same directory, so I don't get why the linker wouldn't be able to link them. I suspect that I might need to set some environment variable, but which one?

Any help would be greatly appreciated! Thanks for your patience - I know this error has been posted here a thousand times before, but I haven't found an answer that works for me.

Upvotes: 2

Views: 96

Answers (2)

daenin
daenin

Reputation: 31

For reference, solution was to add a dummy main to Num.cpp in order to compile with g++.

#include "Num.h" 
int main(){}  
Num::Num(int n): num(n) {} 
int Num::getNum() {  return num; }

Upvotes: -1

MikeCAT
MikeCAT

Reputation: 75062

By default you need main function, from which program execution starts from there, to build executable binary file.

You can use -c option like

g++ -c Num.cpp

to do compilation only (no linking) and get an object file Num.o.

Upvotes: 2

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