Converting a char array to an int in C

Avoid atoi()

It’s easy to work with atoi(), but you have to be sure that what you want to convert is a char array that only contains numbers and not any other characters (symbols, for example).

Passing a char such as e to atoi() will result in undefined behavior. Error handling can get a bit messy.

Use strtol() instead

long int strtol (const char* str, char** endptr, int base)

In summary, the first parameter is the string (char array), the second can be ignored by passing NULL, and the final one is the number base (usually 10).

There are some interesting things that you can do with this function, such as splitting a string into text and numbers.

A simple example

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

int main() {
  char str[] = "123";

  int num = strtol(str, NULL, 10);

  printf("%d", num);
  return 0;
}