Best scope questions in November 2011

Why is my HelloWorld function not declared in this scope?

Asked on Tue, 22 Nov 2011 by IMAPC c++ scope
29 votes 
#include <iostream>

using namespace std;

int main()
{
    HelloWorld();
    return 0;
}

void HelloWorld()
{
    cout << "Hello, World" << endl;
}

I am getting the following compilation error with g++:

l1.cpp: In function 'int main()':
l1.cpp:5:15: error: 'HelloWorld' was not declared in this scope

Answered by Mysticial

You need to either declare or define the function before you can use it. Otherwise, it doesn't know that HelloWorld() exists as a function.

Add this before your main function:

void HelloWorld();

Alternatively, you can move the definition of HelloWorld() before your main():

#include <iostream>
using namespace std;

void HelloWorld()
{
  cout << "Hello, World" << endl;
}

int main()
{
  HelloWorld();
  return 0;
}