Using namespace c++

Dev Zone Code
1

Hello I'm trying to wrap my head around how namespace works. After reading about it I build a super simple program to test my understanding. Unfortunately I'm getting a multiple definition error and not sure why. Here is my program. 

include <iostream>
include "file_one.cpp"
using namespace std;

int main()
{
    int x = 2;
    int y = 1;
    cout << file_one::addNum(x,y);
}

* file_one.cpp

namespace file_one{
    int addNum(int num1, int num2){           <<<** getting the error here**
        int total;
        total =  num1 + num2;
        return total;
    }
}
2

You don't include file_one.cpp! That's another compilation unit that will be compiled before you call the function (must tell the compiler to compile that cpp file too). You have to have a header file add the declaration of function there. The compiler is yelling at you that there's already one function called file_one::addNum

So you will end up with something like this (3 files):

  • Your main.cpp

int main() 
{
   // your code... 
}
  • Your function.h

namespace file_one
{
    int add_num(int, int);
}
  • Your function.cpp

using namespace file_one;
int add_num(int a, int b) 
{
 // your code.
}
3

namespaces are essentially function grouping.

its there to prevent naming collisions.

now in practice it will requires working with header files and other CPP files which can get a bit confusing for beginnres.

I would post eamples but dude above me did a good job of it.

4

cool thanks!