> For the complete documentation index, see [llms.txt](https://docs.1l.lol/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.1l.lol/functions/scope.md).

# 变量作用域

### 全局变量与局部变量

* **全局变量**：定义在所有函数之外，整个程序都可以访问，默认值为 0。
* **局部变量**：定义在函数或语句块内，只在该范围内有效。

```cpp
#include <iostream>
using namespace std;

int g = 10;          // 全局变量

void f() {
    int g = 20;      // 局部变量，遮蔽了全局变量
    cout << g << endl;  // 20
}

int main() {
    cout << g << endl;  // 10
    f();
    {
        int x = 5;   // 仅在花括号内有效
        cout << x;
    }
    // cout << x;    // 错误：x 已失效
    return 0;
}
```

### 作用域与生命周期

|      | 全局变量 | 局部变量   |
| ---- | ---- | ------ |
| 作用域  | 整个文件 | 定义所在的块 |
| 生命周期 | 整个程序 | 块执行期间  |
| 默认初值 | 0    | 不确定    |

### 使用建议

* 尽量少用全局变量，避免命名冲突。
* 大数组开了要清零时，放全局可以自动为 0（也可静态初始化）。
* 局部变量一定要先初始化再使用。


---

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