C/C++ 中的 extern 的變數範例

資料來源: https://medium.com/@alan81920/c-c-%E4%B8%AD%E7%9A%84-static-extern-%E7%9A%84%E8%AE%8A%E6%95%B8-9b42d000688f

CodeBlocks 12.11

module1.cpp

#include <iostream>
#include "module1.h"

using namespace std;

int a = 1;
void greeting() {
    cout << "Hello World!" << endl;
    cout << "In greeting, a = " << a << endl;
}

module1.h

#ifndef MODULE1_H_INCLUDED
#define MODULE1_H_INCLUDED

extern int a;
void greeting();

#endif // MODULE1_H_INCLUDED 

main.cpp:

#include <iostream>
#include "module1.h"

using namespace std;

int main() {
    greeting();
    cout << "In main, a = " << a << endl;
    cout << endl;
    a = 0;
    cout << "In main, a = " << a << endl;
    greeting();
    return 0;
}
/*
Hello World!
In greeting, a = 1
In main, a = 1

In main, a = 0
Hello World!
In greeting, a = 0
*/