cstringatoi

How to convert a string to integer in C?

I am trying to find out if there is an alternative way of converting string to integer in C.

I regularly pattern the following in my code.

char s[] = "45";

int num = atoi(s);

So, is there a better way or another way?

Solution

  • There is strtol which is better IMO. Also I have taken a liking in strtonum, so use it if you have it (but remember it's not portable):

    long long
     strtonum(const char *nptr, long long minval, long long maxval,
     const char **errstr);

    You might also be interested in strtoumax and strtoimax which are standard functions in C99. For example you could say:

    uintmax_t num = strtoumax(s, NULL, 10);
if (num == UINTMAX_MAX && errno == ERANGE)
    /* Could not convert. */

    Anyway, stay away from atoi:

    The call atoi(str) shall be equivalent to:

    (int) strtol(str, (char **)NULL, 10)

    except that the handling of errors may differ. If the value cannot be represented, the behavior is undefined.