C - 数组未填充时 fgets 挂起答案

【问题标题】：C - fgets hangs when array not filledC - 数组未填充时 fgets 挂起
【发布时间】：2015-01-13 11:08:26
【问题描述】：

我正在从stdin 和fgets() 获取输入，并且似乎在缓冲区溢出方面遇到了一些麻烦。我添加了一个 while 循环，该循环旨在吃掉所有字符，但是我的代码运行了多次，并且应该只运行一次。

void play_game(void) {
    int ch; /* Waste */
    /* Max input from fgets */
    char c[8];

    enum cell_contents board[BOARD_HEIGHT][BOARD_WIDTH];

    init_board(board);

    while(!is_game_over(board)) {
        display_board(board);

        printf("Please enter a move [enter Q or ctrl-D to quit]: ");

        if(fgets(c, sizeof(c), stdin)) {
            printf("Entered: %s\n", c);
            struct move calculated_move = calculate_move(c);

            if(is_valid_move(calculated_move, board))
                player_move(calculated_move, board);
            else
                printf("That is an invalid move!\n");
        }

        /* eat excess data */
        if (strlen(c) == sizeof(c)-1)
            while((ch = fgetc(stdin)) != '\n' && ch != EOF);

        /* eat overfilled data */
        //read_rest_of_line();

    }

    printf("Game over!\n");
    game_over(board);
}

这是我的结果：

Please enter a move [enter Q or ctrl-D to quit]: E4, C4 gfgfd oigjdfogkf dohdfkho dk
Entered: E4, C4 
            +---+---+---+        
1           | o | o | o |        
            +---+---+---+        
2           | o | o | o |        
    +---+---+---+---+---+---+---+
3   | o | o | o | o | o | o | o |
    +---+---+---+---+---+---+---+
4   | o | . | o | . | . | o | o |
    +---+---+---+---+---+---+---+
5   | o | o | o | o | o | o | o |
    +---+---+---+---+---++---+---+
6           | o | o | o |        
            +---+---+---+        
7           | o | o | o |        
            +---+---+---+        
      A   B   C   D   E   F   G   
Please enter a move [enter Q or ctrl-D to quit]: Entered: gfgfd o
That is an invalid move!
            +---+---+---+        
1           | o | o | o |        
            +---+---+---+        
2           | o | o | o |        
    +---+---+---+---+---+---+---+
3   | o | o | o | o | o | o | o |
    +---+---+---+---+---+---+---+
4   | o | . | o | . | . | o | o |
    +---+---+---+---+---+---+---+
5   | o | o | o | o | o | o | o |
    +---+---+---+---+---++---+---+
6           | o | o | o |        
            +---+---+---+        
7           | o | o | o |        
            +---+---+---+        
      A   B   C   D   E   F   G   
Please enter a move [enter Q or ctrl-D to quit]: Entered: igjdfog
That is an invalid move!
            +---+---+---+        
1           | o | o | o |        
            +---+---+---+        
2           | o | o | o |        
    +---+---+---+---+---+---+---+
3   | o | o | o | o | o | o | o |
    +---+---+---+---+---+---+---+
4   | o | . | o | . | . | o | o |
    +---+---+---+---+---+---+---+
5   | o | o | o | o | o | o | o |
    +---+---+---+---+---++---+---+
6           | o | o | o |        
            +---+---+---+        
7           | o | o | o |        
            +---+---+---+        
      A   B   C   D   E   F   G   
Please enter a move [enter Q or ctrl-D to quit]:

【问题讨论】：

fgets 不会写入超出缓冲区的末尾，只要您给它一个正确的大小。但是，如果它适合缓冲区，它可以添加换行符。
至于您的问题，请尝试在调试器中逐行执行代码，同时注意变量及其内容。它可能会帮助您找出问题所在。
另外，小心那个循环吃掉剩余的字符。如果用户输入了 6 个字符和一个换行符怎么办？那么strlen(c) == sizeof(c) - 1 也将成立，您将从 next 行开始读取字符（或者更确切地说，游戏似乎在fgetc 等待输入时锁定）。更好的检查是缓冲区中的最后一个字符是否为换行符。
如果从stdin 中删除消耗剩余字符的循环会发生什么？
我将如何处理这个约阿希姆？

标签： c fgets

【解决方案1】：

通过检查数组中的最后一个字符是否为新行来解决问题。

/* eat excess data */
if (strlen(c) == sizeof(c)-1 || c[sizeof(c)-1] != '\n')
    read_rest_of_line();

void read_rest_of_line(void){
    int ch;
    /* remove all characters from the buffer */
    while (ch = getc(stdin), ch != '\n' && ch != EOF);

    /* clear the error status of the input pointer */
    clearerr(stdin);
}

【讨论】：