How to convert a string to integer in C?

Question

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?

Accepted Answer

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.

How to convert a string to integer in C?

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