CODEWITHSUNDEEP
cintegerstrtol
Shou Barrett
Shou Barrett

Reputation: 61

How to extract various integers from a string in C?

I was wondering how to extract various numbers from a string. I understand that strtol works, however it appears to only work for the first digit.

Here is my code

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

int main(){
    long v1, v2, v3;
    char str[20] = "16,23";
    char *d;
   v1 = strtol(str, &d, 10);
   v2 = strtol(str, &d, 10);
   printf("string is %s\nv1 is:%i\nv2 is:%d\n",str , v1,v2);
   return 0;
}

In this example I would like to output v1 = 16 and v2 = 23.

Another example, if the str was "12,23,34", I would like v3= 34

Thanks in advance :)

Upvotes: 1

Views: 1505

Answers (3)

chux
chux

Reputation: 153457

Use long strtol(const char * nptr, char ** endptr, int base). The endptr allows for easy subsequent parsing as that is where parsing stopped.

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

int string_to_longs(const char *s) {
  #define N 3
  long v[N];
  int i;
  for (i=0; i<N; i++) {
    errno = 0;
    char *end;
    v[i] = strtol(s, &end, 10);

    if (errno) return -1; // overflow
    if (s == end) return -1; // no conversion
    printf("v[%d] = %ld\n", i, v[i]);
    if (*end == 0) break; // we are done
    if (*end != ',') return -1; // missing comma
    s = (const char *) (end + 1);
  }
  return i;
}

int main(void) {
  string_to_longs("16,23");
  string_to_longs("12,23,34");
  return 0;
}

Upvotes: 2

vdaras
vdaras

Reputation: 352

strtol just converts a character array to a long int. It stops when it finds the first character that wouldn't make sense into interpreting an integer from.

There is a function in string.h named strtok which helps you tokenize a string.

Beware that strtok mutates the original character array contents.

Upvotes: 1

Sourav Ghosh
Sourav Ghosh

Reputation: 134326

You can have many approaches. One of them is to make use of the endptr, populated by the previous strtol() call as the source of the next strtol().

Otherwise, for a better and flexible approach, you also have an option of using strtok() with a predefined delimiter (the , here) to get the tokens one by one and convert them to int or long (as you wish) until strtok() returns NULL.

Upvotes: 2

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