Thread: Question about making a C++ archive (.a file)

I am confused by how to make a archive. Here is the code I use:

I first have a vector.h file

Code:

//vector.h
namespace TEST{
  int add(int x, int y);
}

Also a vector.cc file contains its definition.

Code:

//vector.cc
#include <iostream>
#include "vector.h"

int TEST::add(int x, int y){
  return (x+y);
}

int main(){
    std::cout<<TEST::add(1,1)<<std::endl;
    return 0;
}

I use the following command to make a libvec.a

g++ -c vector.cc
ar rcs libvec.a vector.o

Then here is the program uses libvec.a

Code:

//main.cc
#include <iostream>
#include "vector.h"

using namespace std;

int main(){
    cout<<TEST::add(2,3)<<endl;
    return 0;
}

So far so good. Finally I use the following command to make main program using libvec.a

Code:

g++ -o main main.cc  libvec.a

It reports:
libvec.a(vector.o)(.text+0xc): In function `main':
: multiple definition of `main'
/tmp/ccRdvIKb.o(.text+0x0): first defined here
collect2: ld returned 1 exit status


I am confused. It seems that I can't define main() function for an archive. But I have seen many code that has main() function but also is compiled for an archive. Anybody has a clue what is wrong?

I believe the way to compile, assuming you have an .A file, is

g++ -I path/to/lib othercode.cc -o executable

In this way, you can keep the lib wherever you store your personal libraries and use #include <lib.hpp>

Assuming the use of g++ implies a Unix/Linux variant: Creating Unix Libraries.