c - 有没有办法在C中读取括号内以逗号分隔的2个整数，忽略空格

Question

我正在读取列表中每一对的键和值，忽略空格并尝试打印它。我的文件包含以下数据:

(2, 50) (4, 30) (9, 30) (10, 400) (-5, -40)
(7, 20) (19, 200) (20, 50) (-18, -200) (-2, 29)
(2, 67) (4, 35) (9, 45) (-18, 100) 

我正在尝试一一获取括号内的整数。例如。

m=2
n=50
m=4
n=30

我尝试从文件中读取数据直到文件结束。扫描并打印 m 和 n 值。

    int m,n;
    FILE* file = fopen("File1.txt", "r"); // open a file
    while (!feof (file))
    {
        fscanf (file, "(%d, %d)", &m, &n);
        printf("m is %d:", m);
        printf("n is %d:", n);
    }
    //close the file after opening
    fclose (file);

运行代码时构建成功，而

m is 2:n is 50:m is 2:n is 50:m is 2:n is 50:m is 2:n is 50:m is 2:n is 50:m is 2:n is 50:m is 2:

无休止地打印而不是从文件中读取整数。

请帮忙。

Answer 1

我看到的错误:首先是误用了feof，第二是输入卡在了第二个'('，其中实际上有一个空格输入数据。您可以通过在格式说明符中添加空格来过滤掉(空白)空格。此外，您应该始终检查文件是否打开。

#include <stdio.h>

int main()
{
    int m,n;
    FILE* file = fopen("File1.txt", "r");
    if(file == NULL) {
        return 1;                                   // error checking
    }
    while (fscanf (file, " (%d,%d)", &m, &n) == 2)  // check for number of conversions
    //   space added here ^    ^ the space here was unnecessary
    {
        printf("m=%d, n=%d\n", m, n);
    }
    fclose(file);
    return 0;
}

程序输出:

m=2, n=50
m=4, n=30
m=9, n=30
m=10, n=400
m=-5, n=-40
m=7, n=20
m=19, n=200
m=20, n=50
m=-18, n=-200
m=-2, n=29
m=2, n=67
m=4, n=35
m=9, n=45
m=-18, n=100

Because feof detects if there was a previous attempt to read beyond the end of the file, which you don't do, the end condition was never met.

---

Edit: answering the comment below, the format string can be made to tolerate additional whitespace anywhere in the input, by adding a space before every specifier that does not automatically filter whitespace. Like this:

fscanf (file, " (%d ,%d )", &m, &n)

格式字符串中每个括号和逗号前面现在有一个空格。每个 %d 之前不需要有空格，因为该格式规范会自动过滤掉前导空格。这对于随机间隔的输入(例如

)可以正确工作

"   (    4  ,  30  )  "