No way to parse integers in C (2022)

I wasn't in this class myself, but one prof at my alma mater started his "Programming 201" class with the simplest assignment: write a C program that accepts two integers from the user and prints their sum. It actually was the only assignment for the rest of the semester, since he has a test suite that would humiliate the students gently at first, but would ultimately pipe a billion nines into stdin as the first argument.

I remember an old project that ran into something like this. I think we just used atoi() or similar and the error check was a string comparison between the original input and a sprintf() of the converted value.

Ugly (and not performant if in a hot path) but it works.

One of the first homework assignments when I learned C back in '83 was after a long lecture on how the string functions are fundamentally broken, and the class introduction to writing C was fixing all of them.

Why not look at how other languages attack this? e.g. how does "42".parse() work in rust?

Edit: https://doc.rust-lang.org/src/core/num/mod.rs.html#1537

interesting! It boils down to this

pub const fn from_ascii_radix(src: &[u8], radix: u32) -> Result<u32, ParseIntError> {

    use self::IntErrorKind::*;

    use self::ParseIntError as PIE;

    // guard: radix must be 2..=36

    if 2 > radix || radix > 36 {

        from_ascii_radix_panic(radix);

    }

    if src.is_empty() {

        return Err(PIE { kind: Empty });

    }

    // Strip leading '+' or '-', detect sign

    // (a bare '+' or '-' with nothing after it is an error)

    // accumulate digits, checking for overflow

    Ok(result)

}

I thought it was pretty well known that everything related to strings in C stdlib (including all str... functions) is bad. You just need to bring in your own string library.

Cant you just:

  for(int i = 0; i < len(characters); i++)
  {
    if(characters[i]-48 <= 9 && characters[i]-48 >= 0)
    {
      ret = ret * 10 + characters[i] - 48;
    }
    else
    {
      return ERROR;
    }
  }
  return ret;

https://man.openbsd.org/strtonum

As a C programmer, I find this kind of bad faith article very irritating.

Yes, the standard library is bad. This is by far the worst part of the C legacy. But it is not that hard to write your own.

String functions like this are not difficult at all, and you can use better naming and semantics, write faster code etc.

C is not the C standard library, ffs.

Another case many integer parsing functions get wrong is that they interpret a leading 0 as an octal indicator.

That should be opt-in via a flag, if it needs to be supported at all. Unix file permissions are the only deliberate use of octal I've ever seen.

Can't you regex that given string contains just numbers and then use any of the provided methods? Then check if the returning value is a number to cater for edge cases

Ok, having a method to do that for you would be nice, but the post reads like it's an issue that std library doesn't provide you with a method behaving as you exactly want

... say users of only language with no way to parse integers.

:)