声明与全局，局部和静态同名的变量 [英] declaration of variables with same name as global,local and static

问题描述

我有以下代码片段，我必须分析输出内容：

I have the following code snippet and I have to analyse what the output will be:

#include <stdio.h>

  void f(int d);

  int a = 1, b = 2, c = 3, d = 4;

  int main(){
    int a = 5, c = 6;
    f(a);
    f(b);
    f(c);
    printf("%d %d %d %d\n",a,b,c,d);
    return 0;
  }

  void f(int d){
    static int a = 0;
    a = a + 7;
    b = a + d;
    c++;
    d--;
    printf("%d %d %d %d\n",a,b,c,d);
  }

我得到的输出如下：

7 12 4 4  
15 26 5 11  
21 27 6 5  
5 27 6 4  

这真的让我感到困惑。我注意到，在所有3个函数调用中，全局声明的 a 都遭受分配，并且在 printf（）中， code> main（）主体在 main（）中声明的 a 是打印。但是，我不确定其余变量的行为。

This really baffled me. I noticed that in all 3 function calls the globally declared a suffers the assignment and that in the printf() from main() body the a declared in main() is printed. However, I am not sure about the behaviour of the rest of the variables. Is this undefined behaviour or it actually makes sense?

推荐答案

int a = 1，b = 2，是真的吗？ c = 3，d = 4； --->全局变量

int main(){
    int a = 5, c = 6;         ---> Shadows the global `a` and `c`

....

void f(int d){
    static int a = 0;         ---> local static variable visible only inside `f`

...

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