How to parse a string separated by commas?

Question

Char *strings = "1,5,95,255"

I want to store each number into an int variable and then print it out.

For example the output becomes like this.

Value1 = 1

value2 = 5

Value3= 95

value4 = 255

And I want to do this inside a loop, so If I have more than 4 values in strings, I should be able to get the rest of the values.

I would like to see an example for this one. I know this is very basic to many of you, but I find it a little challenging.

Thank you

@KerrekSB I thought it was in the POSIX realtime extensions. (specifically POSIX.1-2001), but you're definitely correct it is not in the standard lib. — WhozCraig, Apr 04 '13 at 22:13
@KerrekSB You are right, it's an extension. However, these days I'd not use `strtok` out of fear that it would break on concurrent use, and roll my own implementation if the `strtok_r` were not available. — Sergey Kalinichenko, Apr 04 '13 at 22:17
Oh, for `strtok` you need a modifiable version of the string, by the way. — Kerrek SB, Apr 04 '13 at 22:21

score 11 · Accepted Answer · edited Jul 05 '19 at 17:55

11

Modified from cplusplus strtok example:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main ()
{
    char str[] ="1,2,3,4,5";
    char *pt;
    pt = strtok (str,",");
    while (pt != NULL) {
        int a = atoi(pt);
        printf("%d\n", a);
        pt = strtok (NULL, ",");
    }
    return 0;
}

edited Jul 05 '19 at 17:55

shantanu pathak

2,018
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answered Apr 04 '13 at 22:17

gongzhitaao

6,566
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2

My id wants to write this as `for (char * pt = strtok(str, ","); pt; pt = strtok(NULL, ",")) { /* ... */ }` ... because every loop is a `for` loop :-) – Kerrek SB Apr 04 '13 at 22:19
@KerrekSB Right :) BTW, you had the second param of ``strtok`` ``NULL``... :P – gongzhitaao Apr 04 '13 at 22:20
Just misspelled! Fixed, thanks. – Kerrek SB Apr 04 '13 at 22:22
3

strtok is dangerous and horrible. Its also not C++. – Stephen Aug 19 '14 at 10:51
@Stephen It's tagged `c`. I'm not saying it's c++ way. – gongzhitaao Aug 19 '14 at 14:58
@gongzhitaao the broader point that strtok is terrible is a fair one. Strtok_r or strtok_s or some such alternative would have been much better. And by just printing the results you skip over all the memory issues and the fact that those resulting strings will get messed up if passed elsewhere ... strtok is frankly a nightmare. – Max von Hippel Sep 29 '16 at 08:44
1

@MaxvonHippel I agree that `strtok` sucks most of the time. However depending on the situation, it may or may not be the best solution. You may need a complete CSV parser sometime. – gongzhitaao Sep 29 '16 at 12:38
@gongzhitaao I made a complete csv parser with strtok_r – Max von Hippel Sep 29 '16 at 15:45
Please include #include – shantanu pathak Jul 05 '19 at 09:57

Edward Goodson · Answer 2 · 2013-04-04T22:42:47.290

I don't know the functions mentioned in the comments above but to do what you want in the way you are asking I would try this or something similar.

char *strings = "1,5,95,255";
char number;
int i = 0; 
int value = 1;

printf ("value%d = ", value);
value++; 

while (strings[i] != NULL) {
   number = string[i];
   i++;
   if (number == ',') 
       printf("\nvalue%d = ",value++);
   else 
       printf("%s",&number);
}

score 0 · Answer 3 · answered Apr 04 '13 at 22:55

If you don't have a modifiable string, I would use strchr. Search for the next , and then scan like that

#define MAX_LENGTH_OF_NUMBER 9
char *string = "1,5,95,255";
char *comma;
char *position;
// number has 9 digits plus \0
char number[MAX_LENGTH_OF_NUMBER + 1];

comma = strchr (string, ',');
position = string;
while (comma) {
    int i = 0;

    while (position < comma && i <= MAX_LENGTH_OF_NUMBER) {
        number[i] = *position;
        i++;
        position++;
    }

    // Add a NULL to the end of the string
    number[i] = '\0';
    printf("Value is %d\n", atoi (number));

    // Position is now the comma, skip it past
    position++;
    comma = strchr (position, ',');
}

// Now there's no more commas in the string so the final value is simply the rest of the string
printf("Value is %d\n", atoi (position)l

How to parse a string separated by commas?

3 Answers3

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