c - 当我们尝试打印 c 中未初始化的变量(可能是全局变量或局部变量)时，会发生什么？

Question

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Is un-initialized integer always default to 0 in c? (4 个回答)

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已关闭 5 年前。

当我们尝试打印 c 中未初始化的变量(可能是全局变量或局部变量)时，会发生什么？在 C 中，变量也由编译器自动初始化为默认值吗？这是我的代码

#include<stdio.h>
int b;
int main()
{
    float a;
    printf("%f %d",a,b);
}

我得到的输出为

0.000000 0

请问谁能解释一下吗？

Answer 1

具有静态存储持续时间的全局变量是隐式初始化的。

除非显式完成，否则不会初始化具有自动存储持续时间的局部变量。但是，如果局部变量具有静态存储类，则会对其进行初始化。

引用C11 ,

If an object that has automatic storage duration is not initialized explicitly,its value is indeterminate. If an object that has static storage duration is not initialized explicitly, then:

— if it has pointer type, it is initialized to a null pointer;

— if it has arithmetic type, it is initialized to (positive orunsigned) zero;

— if it is an aggregate, every member is initialized (recursively) according to these rules;

— if it is a union, the first named member is initialized (recursively) according to these rules.