does function location in c++ matter?

Question

#include <iostream>
using namespace std;
int my_variable = 12;
void cappy()
{
    std::cout<<"value is"<< my_variable<<endl;
}

int main()
{
std::cout<< my_variable<<endl;
cappy();
}

this c++ code work and returns:

12
value is12

but whereas :

#include <iostream>
using namespace std;
int my_variable = 12;

int main()
{
std::cout<< my_variable<<endl;
cappy();
}

void cappy()
{
    std::cout<<"value is"<< my_variable<<endl;
}

this code returns an error:

cpp: In function ‘int main()’:
cpp:8:7: error: ‘cappy’ was not declared in this scope

why is this so? does location of functions matter in c++?

possible duplicate of [What is the difference between a definition and a declaration?](http://stackoverflow.com/questions/1410563/what-is-the-difference-between-a-definition-and-a-declaration) — Daniel Frey, Apr 19 '14 at 06:42
Good question man, thinking critically and practicing like you are is the best way to learn! — ultifinitus, Apr 19 '14 at 06:48

score 5 · Answer 1 · answered Apr 19 '14 at 06:39

5

The function needs to be declared before it is used. Besides that, it doesn't matter. So you can have this:

void cappy(); // declaration

int main()
{
  cappy();
}

void cappy() // definition
{

}

answered Apr 19 '14 at 06:39

juanchopanza

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score 0 · Answer 2 · answered Apr 19 '14 at 06:47

It happens because in c++ the compiler reads through the file once and isn't "smart enough to know" that this is a future function that is being called. So you could declare the function earlier, or make a header file declaring all the functions you will be using.

does function location in c++ matter?

2 Answers2