C: scanf 输入单个字符并验证 [英] C: scanf input single character and validation

问题描述

我在 C 中验证单字符 scanf 输入时遇到问题，但找不到有效的现有解决方案...

I've encountered a problem when validating a single-char scanf input in C and I cannot find an existing solution that works...

场景是:一个方法正在接受单个字母'char'类型的输入，然后验证这个输入，如果不满足条件，则弹出错误消息并重新输入，否则返回此字符值.

The scenario is: a method is taking a single letter 'char' type input and then validating this input, if the criteria is not met, then pops an error message and re-enter, otherwise return this character value.

我的代码是:

char GetStuff(void)
{
    char c;
    scanf("%c", &c);
    while(c != 'A' || c != 'P')
    {
          printf("invalid input, enter again (A for AM or P for PM): ");
          scanf ("%c", &dtChar);
    }
    return c;
}

但是，无论我输入什么输入，我都会收到无限循环的错误消息.我阅读了其他一些帖子，猜测是 %c 说明符在我按下 Enter 键时没有自动摆脱换行符的问题，所以到目前为止我已经尝试过:

however, i got the infinite loop of error message no matter what input I type in. I read some other posts and guess it's the problem that %c specifier does no automatically get rid of the newline when I hit enter, and so far I have tried:

1. 在 %c 之前/之后放置一个空格，例如:

1. putting a white space before/after %c like:

scanf(" %c", &c);

编写一个单独的方法或包含在这个 GetStuff 方法中来清理换行符，例如:

write a separate method or include in this GetStuff method to clean the newline like:

void cleanBuffer(){
  int n;
  while((n = getchar()) != EOF && n != '\n' );
}

有人可以帮我解决这个问题吗?提前致谢.

Can anyone help me with this problem please? Thank you in advance.

推荐答案

#include <stdio.h>

char GetStuff(void) {
    char c;
    scanf("%c", &c);
    getchar();
    while ((c != 'A') && (c != 'a') && (c != 'P') && (c != 'p')) {
        printf("invalid input, enter again (A for AM or P for PM): ");
        scanf ("%c", &c);
        getchar();
    }
    return c;
}

int main(void) {
    printf("Calling GetStuff()...\n");
    char x = GetStuff();
    printf("User entered %c\n", x);
    return 0;
}

您使用 while (c != 'A' || c != 'P') 作为循环条件，但这将始终返回 true.您要使用的是 &&和"运算符，而不是 ||或"运算符.

You are using while (c != 'A' || c != 'P') as your loop conditional, but this will always return true. What you meant to use is the && "and" operator, instead of the || "or" operator.

此外，在 scanf 语句之后调用 getchar() 以捕获换行符.这应该按照您希望的方式工作.

Also, call getchar() after your scanf statements, to capture the newline. This should work the way you want it to.

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