C 中的全局和局部变量

Global and local variables in C++

本文关键字：局部变量 全局      更新时间：2023-10-16

我是C 的新手，在打印本地和全局变量时，我会遇到一些问题。考虑这件简单的代码：

#include <cstdlib>
#include <iostream>
using namespace std;
/*
 * 
 */
int x = 10; // This x is global
int main() {
    int n;
    { // The pair of braces introduces a scope  
    int m = 10;    // The variable m is only accessible within the scope
    cout << m << "n";
    int x = 25; // This local variable x hides the global x
    int y = ::x; // y = 10, ::x refers to the global variable x
    cout << "Global: " << y << "n" << "Local: " << x << "n";
    {
        int z = x; // z = 25; x is taken from the previous scope
        int x = 28; // it hides local variable x = 25 above
        int t = ::x; // t = 10, ::x refers to the global variable x
        cout << "(in scope, before assignment) t = " << t << "n";
        t = x; // t = 38, treated as a local variableout was not declared in this scope
        cout << "This is another hidden scope! n";
        cout << "z = " << z << "n";
        cout << "x = " << x << "n";
        cout << "(in scope, after re assignment) t = " << t << "n";
    } 
    int z = x; // z = 25, has the same scope as y
    cout << "Same scope of y. Look at code! z = " << z;
    }
    //i = m; // Gives an error, since m is only accessible WITHIN the scope
    int m = 20; // This is OK, since it defines a NEW VARIABLE m
    cout << m;
    return 0;
}

我的目标是练习各个范围内变量的可访问性，然后打印它们。但是，我无法弄清楚为什么当我尝试打印最后一个变量z时，NetBeans会给我提供输出2025。在这里，它遵循我的样本输出：

10
Global: 10
Local: 25
(in scope, before assignment) t = 10
This is another hidden scope! 
z = 25
x = 28
(in scope, after re assignment) t = 28
Same scope of y. Look at code! z = 2520
RUN FINISHED; exit value 0; real time: 0ms; user: 0ms; system: 0ms

希望有人可以帮助我了解发生了什么！：）

不是 z> z 保持值 2520 是您要添加的事实是，您可以在printing z 和打印 m ...

您正在做：

cout << "Same scope of y. Look at code! z = " << z;
}
int m = 20;  
cout << m;

但是您应该这样做：

std::cout << "Same scope of y. Look at code! z = " << z << std::endl;
}
int m = 20;  
std::cout << m << std::endl;

如果您只是遵循标签输出并执行

的相同标准 
std::cout << "M is: "<<m << std::endl;

您会通过观察输出来更快地发现问题：

25M is: 20
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