C - 有没有办法读取用户输入的单个字符，而不是让其余的“下推”到下一个输入请求？

Question

所以，我正在用 C 语言开发一个简单的刽子手游戏，并且我有 read_guess 函数，如下所示。

void read_guess(char *guesses, char *p_current_guess)
{
    int valid_guess = 0;

    // Repeatedly takes input until guess is valid
    while (valid_guess == 0)
    {
        printf(">>> ");
        fgets(p_current_guess, 2, stdin);

        if (!isalpha(*p_current_guess)) printf("Guesses must be alphabetic. Please try again.\n\n");
        else
        {
            valid_guess = 1;

            // Iterates over array of guesses and checks if letter has already been guessed
            for (int i = 0; guesses[i] != '\0'; i++)
            {
                if (guesses[i] == *p_current_guess)
                {
                    printf("You have already guessed this letter. Please try again.\n\n");
                    valid_guess = 0;
                    break;
                }
            }
        }
    }
}

我已经尝试了所有标准输入函数（包括 getchar），但是对于所有这些函数，当提供大于一个字符的输入时，而不是只取第一个字符并继续（或再次询问），输入的其余部分被“推回”，并且下一次请求输入时，无论是因为输入包含非字母字符还是下一轮开始，输入的其余部分都会自动处理。这对输入的每个字符重复。

我怎样才能避免这种情况？

Answer 1

您正在使用fgets，这很好，但不幸的是不是正确的方式......

fgets 读取到行尾或最多 1 减去所询问的字符数。当然剩下的字符留给下一次读取操作......

惯用的方法是确保阅读到行尾，无论长度如何，或者至少达到更大的长度。

1. 简单但在输入超过 SIZE 个字符时可能会失败：

   #define SIZE 64
   ...
   
   void read_guess(char *guesses, char *p_current_guess)
   {
       char line[SIZE];
       int valid_guess = 0;
   
       // Repeatedly takes input until guess is valid
       while (valid_guess == 0)
       {
           printf(">>> ");
           fgets(line, SiZE, stdin);                // read a line of size at most SIZE-1
           p_current_guess[0] = line[0];            // keep first character
           p_current_guess[1] = '\0';
           ...
   

2. 强大但稍微复杂一些

   /**
    * Read a line and only keep the first character
    *
    * Syntax: char * fgetfirst(dest, fd);
    *
    * Parameters:
    *  dest: points to a buffer of size at least 2 that will recieve the
    *         first character followed with a null
    *  fd  : FILE* from which to read
    *
    * Return value: dest if one character was successfully read, else NULL
    */
   char *readfirst(dest, fd) {
   #define SIZE 256              // may be adapted
       char buf[SIZE];
       char *cr = NULL;          // return value initialized to NULL if nothing can be read
       for (;;) {
           if(NULL == fgets(buff, sizeof(buff), fd)) return cr; // read error or end of file
           if (0 == strcspn(buff, "\n")) return cr;             // end of file
           if (cr == NULL) {                                    // first read:
               cr = dest;                        //  prepare to return first char
               dest[0] = buff[0];
               dest[1] = 0;
           }
       }
   }
   

   然后您可以在代码中简单地使用它：

   void read_guess(char *guesses, char *p_current_guess)
   {
       int valid_guess = 0;
   
       // Repeatedly takes input until guess is valid
       while (valid_guess == 0)
       {
           printf(">>> ");
           fgetfirst(p_current_guess, stdin);
   

Answer 2

您可以丢弃所有输入直到行尾，每次您想请求输入时。

void skip_to_eol(FILE* f, int c)
{
    while (c != EOF && c != '\n')
        c = fgetc(f);
}
...
    char c = getchar(); // instead of fgets
    skip_to_eol(stdin, c);

Answer 3

您可以在 windows 上使用 getch() 函数来获取单个字符。这是 linux 的等价物

What is the equivalent to getch() & getche() in Linux?