c - 如何定义 `getchar()` 的返回类型？

Question

这个问题已经有答案了:

Why must the variable used to hold getchar's return value be declared as int? (4 个回答)

已关闭 7 年前。

这是代码:

#include <stdio.h>
int main()
{
    char c;
    while((c = getchar()) != EOF) 
    {
        putchar(c);
    }
    return 0;
}

但是有人说我应该改变char c至int c .

谁能告诉我原因？

Answer 1

因为 getchar() 定义为:

 int getchar(void);

这应该是足够的理由。原因解释的很好here :

如果将 getchar 的返回值分配给 char，则可能会出现两种类型的错误/失败。

If type char is signed, and if EOF is defined (as is usual) as -1, the character with the decimal value 255 ('\377' or '\xff' in C) will be sign-extended and will compare equal to EOF, prematurely terminating the input.

If type char is unsigned, an actual EOF value will be truncated (by having its higher-order bits discarded, probably resulting in 255 or 0xff) and will not be recognized as EOF, resulting in effectively infinite input.