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?

You need to remove your "main" from "vector.cc", since the linker will use all the code in vector.o from libvec.a when it links the executable, it will include the second main, which is now "competing" with your main.cc's main() function.

--
Mats

Thanks. One more question:
To make an archive (aka static library), must I use

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

?
Can I use

g++ -o libvec.a vector.cc

?

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.

Code:

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

is the right way to create a library. Of course, you don't want to use c every time you add a object file to the library [the whole point is that you can have a collection of loosely related object files in one library - and then the linker can "borrow" any object that it needs, but it doesn't have to use all of the library].

--
Mats