Code can't get an n-digit numbers from a string in C

Question

I wanna ask how it can not get integer from a string

for example, here are my code:

int main() {
    char str[] = "ababbababa-1998";
    int nr = atoi(str);
    printf("%d\n", nr);
    return (EXIT_SUCCESS);
}

when running, it print out 0 but not 1998, how can I fix it ?

No, i want to put 1998 to the nr variable, not get a single character and convert — STEPHEN bui, Dec 01 '16 at 04:36
You can store all the numbers in a char[] and then convert it into an integer. — Denis, Dec 01 '16 at 04:37
If string format is fixed (like, "some_string-sume_number"), then you can use sscanf(string, "%s-%d", temp_str, &nr)); — MayurK, Dec 01 '16 at 04:57
@STEPHENbui See my updated answer below. It is a simple approach to this problem. — RoadRunner, Dec 01 '16 at 05:45

score 1 · Accepted Answer · edited May 23 '17 at 12:24

1

In your case you can use strtok.

int main() {
    char str[] = "ababbababa-1998";
    char * const first_part = strtok(str, "-");
    if (first_part == NULL) {
        return 1;
    }
    char * const second_part = strtok(NULL, "-");
    if (second_part == NULL) {
        return 1;
    }
    int nr = atoi(second_part);
    printf("%d\n", nr);
    return 0;
}

You can look at Why is there no strtoi in stdlib.h? for error check atoi.

edited May 23 '17 at 12:24

Community

1
1

answered Dec 01 '16 at 04:48

Stargateur

24,473
8
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Is your strtok(str) usage valid? – MayurK Dec 01 '16 at 04:53
Wouldn't it be more robust to just go through the string looking for the first digit rather than relying on `strtok`? – John3136 Dec 01 '16 at 04:54
@MayurK yep I totally forget the delimiter – Stargateur Dec 01 '16 at 04:55
@John3136 if there is a digit in the string before "-", that will fail. I choice strtok to show him a very simple way to do a parser. – Stargateur Dec 01 '16 at 04:58
1

@Stargateur Not enough info has been provided for either of us to know we're right. – John3136 Dec 01 '16 at 05:16
@Stargateur i don't understand at line 7, why strtok(NULL,"-") but not strtok(str,"-") ? – STEPHEN bui Dec 02 '16 at 02:27
@STEPHENbui read the man of strtok. you only need to give one time the str that you want to parse to strtok after it will give you the rest at each call. If strtok send you NULL, there is nothing left. – Stargateur Dec 02 '16 at 02:59

score 1 · Answer 2 · answered Dec 01 '16 at 05:07

Keep walking down str() until code finds something numeric using strtol().

int main() {
    char str[] = "ababbababa-1998";
    char *p = str; 

    char *endptr;
    while (*p) {
      long number = strtol(p, &endptr, 10);
      // Was conversion successful?
      if (endptr != p) {
        printf("%ld\n", number);
        return EXIT_SUCCESS;
      }
      p++;
    }
    puts("No conversion");
    return EXIT_FAILURE;
}

RoadRunner · Answer 3 · 2016-12-01T05:34:40.070

0

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

#define ASCII '0'

int
main(void) {
    char const str[] = "ababbababa-1998";
    int i, result = 0;

    for (i = 0; str[i]; i++) {
        if (isdigit(str[i])) {
            result *= 10;
            result += str[i] - ASCII;
        }
    }

    printf("number = %d\n", result);

    return 0;
}

edited Dec 01 '16 at 05:34

answered Dec 01 '16 at 04:57

RoadRunner

25,803
6
42
75

It may be worth using a larger `INITSIZE` (e.g. 128, 256, etc..) and use a static buffer to avoid the `malloc`, `realloc` overhead. (there isn't anything wrong with dynamic allocation, it just adds overhead and complexity). You may also want to stop adding to `nr` after you have found digits, and then find a subsequent non-digit. (e.g. if you had a string `"aaaaa-1998aaaaa-1999"`) You could use a simple flag for that purpose. Just thoughts, not criticisms. – David C. Rankin Dec 01 '16 at 05:03
Yeah thanks for suggestion @DavidC.Rankin, I think this approach is too complicated. I will edit my answer. – RoadRunner Dec 01 '16 at 05:04
Copy most of the string just to convert it to a number? Rubbish! `if (isdigit(array[i]) { total *= 10; total += array[i]; }` – John3136 Dec 01 '16 at 05:19
Changed it @John3136. I overlooked this simple approach, cheers. – RoadRunner Dec 01 '16 at 05:34
1

Obviously that should be `total += array[i] - '0';` - Just notcied you already did that. – John3136 Dec 01 '16 at 08:20

score 0 · Answer 4 · answered Aug 25 '19 at 05:28

If you want to extract all the numeric digits from a string you could use this function I created.

You will need these header files for this function to work.

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

void getNumbers(char data[]) {
   int index = 0;
   char current;

   for( int i = 0; i < strlen(data); ++i ) {
      current = data[i];
      if (current >= 48 && current <= 57) {
         data[index++] = current;
      }
   }
    data[index] = '\0';
}

You can use the above function like this.


char foobar[] = "1A2B3C4D5E6F7G8H9I";

getNumbers(foobar);

printf("%s", foobar);

The above code will output 123456789

Code can't get an n-digit numbers from a string in C

4 Answers4