程序在不允许输入的情况下跳过 fgets [英] Program is skipping fgets without allowing input

问题描述

基本上正如标题所说.. 当我的程序从控制台运行时，它会询问您是要加密还是解密.. 当我输入 e 或 E 时，它会创建一个新的空行(直到我输入了某种文本)，然后同时显示输入文本"和输入密钥"行..

Basically as the title says.. When my program is run from the console, it'll ask if you'd like to encrypt or decrypt.. and when I input e or E, it creates a new blank line (until I input some kind of text), then shows the "enter the text" and "enter the key" lines all at once..

所以，在控制台中它看起来像:

So, in the console it would look something like:

您想要 (E) 加密还是 (D) 加密?

Would you like to (E)ncrypt or (D)ecrypt? e

asdf jkl;<---- 随机用户输入以使程序继续..

asdf jkl; <---- random user input to get the program to continue..

输入您要加密的文本:输入用于加密的密钥:(用户输入)

Enter the text you would like to encrypt : Enter a key to use for encryption : (user input)

然后程序退出..

//message to be encrypted
char text[250]; 
//word to use as the key
char key[50];
//stores the encrypted word
char encrypted[250];

char answer;
printf("Would you like to (E)ncrypt or (D)ecrypt? ");
scanf(" %c", &answer);

if(answer == 'e' || answer == 'E')
{
    printf("Enter the text you want to encrypt : ");
    fgets(text, 250, stdin);

    printf("Enter a key to use for encryption : ");
    fgets(key, 50, stdin);

    printf("Encrypted text : ");

    //code that encrypts the text here      
}

那么，问题在于它完全跳过了 fgets 而不是等待/允许用户输入任何答案..为什么?

So the problem, then, is that it's skipping the fgets entirely and not waiting/allowing the user to input any answers.. why for?

推荐答案

行 scanf(" %c", &answer); 在fgets 获取的输入缓冲区." %c" 中的前导空格消耗前导 空格而不是尾随 空格.

The line scanf(" %c", &answer); is leaving a newline in the input buffer which is taken by fgets. The leading space in " %c" consumes leading whitespace but not trailing whitespace.

您可以使用 "%*c" 格式说明符去除 newline 在 scanf 中读取 newline 但丢弃它.无需提供 var 参数.

You can get rid of the newline with the "%*c" format specifier in scanf which reads the newline but discards it. No var argument needs to be supplied.

#include <stdio.h>

int main(void)
{
    char answer;
    char text[50] = {0};
    scanf(" %c%*c", &answer);
    fgets(text, sizeof text, stdin);
    printf ("%c %s
", answer, text);
    return 0;
}

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