无法编辑外部变量

Question

我写了以下代码

head.h

int i = 0;

sample.cpp的

#include <stdio.h>
#include "head.h"

extern int i;
i = 20;

int main() {
    printf("%d \n",i);
    return 0;
}

当我编译sample.cpp时，编译器抛出以下错误：

sample.c:5:1: warning: data definition has no type or storage class [enabled by default]
sample.c:5:1: error: redefinition of ‘i’
head.h:1:5: note: previous definition of ‘i’ was here

Answer 1

反过来说，extern声明应该在标题中，定义在实现文件中，只定义一次。

//head.h
extern int i;


//sample.cpp
#include <stdio.h>
#include "head.h"

int i = 20;

int main() {
    printf("%d \n",i);
    return 0;
}

您可以根据需要声明变量，但定义必须是唯一的。