使用％d扫描字符 [英] Scanf a char using %d

问题描述

下面我有一个特定的示例，如果输入整数(请参见output1)，该示例就可以很好地工作，当我尝试在scanf函数调用中使用％d说明符扫描char时，我得到下面的output2.

I have a specific example below, which works perfectly fine if integers are inputted (see output1), when I try to scan a char using %d specifier in scanf function call I get the output2 below.

所以，我的问题是，如果输入一个char，我希望类型说明符将其转换为等效的int值(如果不是垃圾值)，即使在任何情况下都应打印/段错误.但是，在这里我得到了连续的打印，这是错误的，因为scanf每次都被绕过.我非常不确定背景中发生了什么，并且想知道相同的情况.

So, my question is if input a char I hope the type specifier should convert it to an equivalent int value, if not a junk value, even in the either case it should print/segfault. But, here I'm getting continuous prints which I feel is wrong as scanf is getting bypassed every single time. I'm pretty unsure what's happening in the background and would like to know the same.

#include <stdio.h>

int main()
{

   int a;

   while (1){
       printf("enter a number:");
       scanf("%d", &a);
       printf("entered number is %d\n", a);
   }

return 0;
}

输出1 :

>     enter a number:1
>     entered number is 1
>     enter a number:
>     3
>     entered number is 3
>     enter a number:4
>     entered number is 4
>     enter a number:5
>     entered number is 5 enter a number:

Output2 :用于输入a

>     enter a number:entered number is 32767
>     enter a number:entered number is 32767
>     enter a number:entered number is 32767
>     enter a number:entered number is 32767
>     enter a number:entered number is 32767
>     enter a number:entered number is 32767
>     enter a number:entered number is 32767
>     enter a number:entered number is 32767
>     enter a number:entered number is 32767

PS:我知道这是一个愚蠢的问题，询问在无效的情况下会发生什么情况，在这种情况下，非预期的类型说明符(在这种情况下为％d)用于不同的类型，但是我想知道在后台发生了什么，如果有的话.谢谢

PS: I know this is a stupid question of asking what happens in an invalid case where a type specifier unintended (%d in this case) is used for different type, but I would like to know what happens in the background, if any. Thanks

推荐答案

您可以将scanf检查为 @chux )

You may check scanf as @Some programmer dude. You may compare the count arguments succesfully filled (Thanks to @chux)

在您的情况下，scanf找不到任何整数值，到达输入的末尾并返回EOF，而使a变量保持不变.

In your case, scanf didn't find any integer value, reached the end of the input and returned EOF, keeping the a variable untouched.

如果失败，它将返回EOF(请阅读 http://www.cplusplus. com/reference/cstdio/scanf/#return ).

On failure it'll return EOF (read http://www.cplusplus.com/reference/cstdio/scanf/#return).

if(scanf("%d", &a) == 1) //Check if exactly one parameter was read. 
    printf("entered number is %d\n", a);

对于字符，最好使用getch()或至少在scanf上要求"%c":

For characters, you better use getch() or at least, ask for "%c" on scanf:

if(scanf("%c", &a) == 1)
    printf("entered key was %d\n", a);

您收到的垃圾"值就是程序存储器中的值，因为a未初始化.

The "junk" value you recieve is what was in your program memory, because a is not initialized.

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