链接和作用域2

header.h

#pragma once
#ifndef HEADER_H
#define HEADER_H

unsigned long returnFactorial(unsigned short num);
unsigned short headerNum = 5;

#endif

that.cpp

#include "header.h"

unsigned short thatNum = 8;
bool printMe = true;

unsigned long returnFactorial(unsigned short num)
{
	unsigned long sum = 1;

	for (int i = 1; i <= num; i++)
	{
		sum *= i;
	}

	if (printMe)
	{
		return sum;
	}
	else
	{
		return 0;
	}
}

this.cpp

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

extern unsigned short thatNum;
static bool printMe = false;

int main()
{
	unsigned short thisNum = 10;

	std::cout << thisNum << "! is equal to " << returnFactorial(thisNum) << std::endl;

	std::cout << thatNum << "! is equal to " << returnFactorial(thatNum) << std::endl;

	std::cout << headerNum << "! is equal to " << returnFactorial(headerNum) << std::endl;

	if (printMe)
	{
		std::cout << "小甲鱼真帅" << std::endl;
	}

	return 0;
}

这里编译后就会提示

说headerNum这个已经在that.cpp里面定义过了，可是明明已经在头文件里面写上那个防止编译的了，还是会这样，所以就是说在头文件里面尽量不要对变量赋值，只要声明就行了。如果一定要赋值的话，就写成static类型。如下：

header.h

#pragma once
#ifndef HEADER_H
#define HEADER_H

unsigned long returnFactorial(unsigned short num);
static const unsigned short headerNum = 5;

#endif

输出结果

ok，完美