Question

I am looking for a (relatively) simple way to parse a random string and extract all of the integers from it and put them into an Array – this differs from some of the other questions which are similar because my strings have no standard format.

Example:

pt112parah salin10n m5:isstupid::42$%&%^*%7first3

I would need to eventually get an array with these contents:

112 10 5 42 7 3

And I would like a method more efficient then going character by character through a string.

Thanks for your help

Answer 1

A quick solution. I’m assuming that there are no numbers that exceed the range of long, and that there are no minus signs to worry about. If those are problems, then you need to do a lot more work analyzing the results of strtol() and you need to detect '-' followed by a digit.

The code does loop over all characters; I don’t think you can avoid that. But it does use strtol() to process each sequence of digits (once the first digit is found), and resumes where strtol() left off (and strtol() is kind enough to tell us exactly where it stopped its conversion).

#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>

int main(void)
{
    const char data[] = "pt112parah salin10n m5:isstupid::42$%&%^*%7first3";
    long results[100];
    int  nresult = 0;

    const char *s = data;
    char c;

    while ((c = *s++) != '\0')
    {
        if (isdigit(c))
        {
            char *end;
            results[nresult++] = strtol(s-1, &end, 10);
            s = end;
        }
    }

    for (int i = 0; i < nresult; i++)
        printf("%d: %ld\n", i, results[i]);
    return 0;
}

Output:

0: 112
1: 10
2: 5
3: 42
4: 7
5: 3