如何修改我的代码以使用 strtol() 而不是 scanf() 仅读取前两个整数？

Question

My current code seems to work fine on DOS but not on Unix, and I need to make it work on both. From what I have found so far, it seems I should use strtol(). However, I cannot seem to figure out how to get strtol() to get only the first two integers.

The input is a text file that looks like this:

45x7
(1,0)
(10,2)

And I need the output to be "There are 45 rows and 7 columns."

This is my current code:

int rows=0, columns=0;
scanf("%d%*c%d%*c", &rows, &columns);
printf("There are %d rows and %d columns.", rows, columns);
return 0;

I do not want to discard the remaining text file as I will need to process that as well.

Answer 1

Here's one way of using fgets and strtol . It is admittedly more verbose than the scanf solution.

int rows=0, columns=0;
char *endp;
char firstline[100];
if(fgets(firstline, sizeof(firstline), stdin) == NULL) {
    fprintf(stderr, "premature EOF\n");
    exit(1);
}
rows = strtol(firstline, &endp, 10);
if(*endp != 'x') {
    fprintf(stderr, "syntax error\n");
    exit(1);
}
columns = strtol(endp + 1, &endp, 10);
if(*endp != '\n') {
    fprintf(stderr, "syntax error\n");
    exit(1);
}
printf("There are %d rows and %d columns.\n", rows, columns);

The key is that strtol 's second argument is a pointer to a pointer which is filled in with a pointer to the first character strtol didn't use. That is, when you pass the string 45x7\n to the first strtol call, it returns 45 , and sets endp to point to the x .