使用fgets刷新标准输入 [英] Flush stdin using fgets

问题描述

尝试通过控制台创建注册页面.我需要几个输入，并且我正在使用fgets，所以我需要刷新stdin.有关堆栈溢出的许多类似问题，都重定向到此处: http://c-faq.com/stdio/stdinflush2.html .我使用该链接获得了下面的代码.但是，这实际上不起作用.它说用户名:"，然后当我输入用户名并按Enter时，它只是转到控制台中的新的空行，我可以在其中输入更多内容.为什么会这样呢?我该如何解决?

Trying to make a registration page through the console. I need several inputs for it, and I'm using fgets, so I need to flush stdin. Lots of similar questions on Stack Overflow redirected here: http://c-faq.com/stdio/stdinflush2.html. I got the code below using that link. However, this doesn't actually work. It says Username:, and then when I type in a username, and press enter, it just goes to a new, empty line in console where I can type in more. Why is this happening? How can I fix it?

添加了代码

NSLog(@"Do you have an account already?(1 for Yes, 0 for no)");
    fgets(cnumb1, 2, stdin);
    int c;
    while((c = getchar()) != '\n' && c != EOF);
    size_t length = strlen(cnumb1);
    if (cnumb1 [length-1] == '\n'){ // In case that the input string has 1 character plus '\n'
        cnumb1 [length-1] = '\0';} // Plus '\0', the '\n' isn't added and the if condition is false.
    NSString* string = [NSString stringWithUTF8String: cnumb1];
    if (string == 0) {
        while(numb4 == 1) {
            numb3 = 1;
            while( numb3 == 1){
                NSLog(@"Username:");
                fgets(usercheck1, 13, stdin);
                int c2;
                while((c2 = getchar()) != '\n' && c2 != EOF);
                size_t length1 = strlen(usercheck1);
                if (usercheck1 [length1-1] == '\n'){ // In case that the input string has 12 characters plus '\n'
                    usercheck1 [length1-1] = '\0';} // Plus '\0', the '\n' isn't added and the if condition is false.

推荐答案

完全改写了我的答案，似乎我对问题的理解不够.

在用户再次按下回车键之前，应该清空输入缓冲区的行将不会得到任何结果-除非用户输入的字符超过了输入缓冲区可以容纳的字符数.

The line that is supposed to empty the input buffer will not get anything until the user presses return again - unless the user enters more characters than the input buffer can hold.

您应该首先检查 fgets 读取的字符串的长度，以及最后一个字符(在 \ 0 之前)是否是 \ n ，请勿尝试阅读更多字符.否则，像您一样清空输入缓冲区.

You should first check the length of string read by fgets and if the last character (before the \0) is a \n, don't try to read more characters. Otherwise empty the input buffer like you did.

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