Using multiple .cpp files in c++ program? - c++

Question

I recently moved from Java for C++ but now when I am writing my application I'm not interested in writing everything of the code in the main function I want in main function to call another function but this other function is in another .cpp file.
Let me explain better if you wouldn't understand:
I have one file: main.cpp inside it I have main function.
I have the second file: second.cpp inside I have a function called second() I want to call this function called second() from my main function..
Any help?

Answer 1

You must use a tool called a "header". In a header you declare the function that you want to use. Then you include it in both files. A header is a separate file included using the #include directive. Then you may call the other function.
other.h
void MyFunc();
main.cpp
#include "other.h"
int main() {
MyFunc();
}
other.cpp
#include "other.h"
#include <iostream>
void MyFunc() {
std::cout << "Ohai from another .cpp file!";
std::cin.get();
}

Answer 2

You should have header files (.h) that contain the function's declaration, then a corresponding .cpp file that contains the definition. You then include the header file everywhere you need it. Note that the .cpp file that contains the definitions also needs to include (it's corresponding) header file.
// main.cpp
#include "second.h"
int main () {
secondFunction();
}
// second.h
void secondFunction();
// second.cpp
#include "second.h"
void secondFunction() {
// do stuff
}

Answer 3

In C/C++ you have header files (*.H). There you declare your functions/classes. So for example you will have to #include "second.h" to your main.cpp file.
In second.h you just declare like this void yourFunction();
In second.cpp you implement it like
void yourFunction() {
doSomethng();
}
Don't forget to #include "second.h" also in the beginning of second.cpp
Hope this helps:)

Answer 4

You can simply place a forward declaration of your second() function in your main.cpp above main(). If your second.cpp has more than one function and you want all of it in main(), put all the forward declarations of your functions in second.cpp into a header file and #include it in main.cpp.
Like this-
Second.h:
void second();
int third();
double fourth();
main.cpp:
#include <iostream>
#include "second.h"
int main()
{
//.....
return 0;
}
second.cpp:
void second()
{
//...
}
int third()
{
//...
return foo;
}
double fourth()
{
//...
return f;
}
Note that: it is not necessary to #include "second.h" in second.cpp. All your compiler need is forward declarations and your linker will do the job of searching the definitions of those declarations in the other files.