在c ++中的两个文件上使用标头？

Question

I have a header file with method names "Sample.h". I have imported this into another file, "methods.cpp" and wrote the code for all the methods in there. Now, I have a third file, "output.cpp" and want to use the methods that I defined in the methods file. Do I just import "Sample.h"?

Answer 1

You've gotten a bunch of noise about include guards and the non-standard #pragma once ; they have nothing to do with using the same header in multiple source files. They give you protection from multiple definition errors when you include the same header more than once in a single source file.

When you need to define functions in one source file and call them from another one, you put function prototypes in a header and include that header in both source files. Like this:

// function.h
#ifndef FUNCTION_H
#define FUNCTION_H
void f();
#endif // FUNCTION_H

// function.cpp
#include "function.h
#include <iostream>
void f() {
    std::cout << "Here I am.\n";
}

// user.cpp
#include "function.h"
int main() {
    f();
    return 0;
}

Answer 2

Yes but best to use something like:

#ifndef MY_SAMPLE__DOT__H__
#define MY_SAMPLE__DOT__H__

... rest of your header

#endif

This will guard against your code being unintentionally included more than once. This is good practice and you should use it all the time in all headers. Wrap all headers in these.

Alternatively use:

#pragma once

As suggested. It isn't standard so may not be supported. More about #pragma once