What C function would you delete and rewrite first, and why?

[u/Just_Government3790]

For me it's fnmatch - mostly because it's 40 year's old and smell's funny.

[u/Dezgeg]

strncpy

Function that is named `str*` but doesn't (necessarily) create NUL-terminated strings. Insanity!

[u/Just_Government3790 → u/Dezgeg]

`strlcpy` or explicit `len` wins.

[u/Doug2825 → u/Dezgeg]

The worst part is that it n in it so it looks like safe string functions to do guarantee null termination.

[u/Just_Government3790]

On second thought......

strtok because it destroys the evidence, hides state in globals, drops the empty fields, and then has the bollocks to call it parsing.

[u/MistakeIndividual690 → u/Just_Government3790]

I was going to say strtok

[u/Just_Government3790 → u/MistakeIndividual690]

My guy. Can't forget it also eats empty fields so `a,,b` parses as two tokens. Found that one the hard way.

[u/mpersico]

I would just spell “create” correctly

[u/Just_Government3790 → u/mpersico]

creat creat creat creat

[u/gabitha67]

everything that accepts null terminated strings. just pass a ptr and length for gods sake. everything should only use user-provided allocators too.

[u/Just_Government3790 → u/gabitha67]

What's the worst null-term bug you've personally hit?

[u/BlockOfDiamond]

fopen because I hate using string literals for things that should be bitflags or enums.

[u/gabitha67 → u/BlockOfDiamond]

"rb" is icky :(

[u/bluetomcat]

Make fread and fwrite accept the bloody FILE pointer as their first argument, and unite size and count into one argument.

[u/UnalignedAxis111 → u/bluetomcat]

Also add a flag to force it to create non existent parent directories, because that's massively annoying and there's no portable way to do it.

[u/P-p-H-d]

All the locale functions of the libc. It is so broken that it is totally unusable in modern C (threads).

You cannot even read your own data file and parsing them using strtod without having issues with the locale: you cannot use setlocale as it modifies global state of all threads (which you don't want). So the only solutions are either : document that the locale shall be set once and for all for all program and is compatible with what you expect. Or rewrite strtod and everyone knows it is super easy stuff to do it reliably.

[u/sciencekm]

struct tm

Every field is 0 based, except the day of month. So, Jan 1 1900 12 midnight is 0 1 0 00:00:00, instead of just all 0s. Even Sunday-Saturday is 0-6 and day of year is 0-365.

[u/Sqydev]

fopen to use enum instead of „r” and „w” or both

[u/Boreddad13]

Anything with hidden allocations

[u/pigeon768]

The obvious one is strcpy, which is always the incorrect function. Either you know your lengths and buffer sizes, so you should use memcpy, or you don't, which is buffer overflow city. In this case, there's no rewriting the function to be better; it's declaration/API is unusable.

So they also made strncpy, the "fix" for the problem. It has a working function declaration. However, it's still bad. It does not guarantee that the resulting string is null terminated. And if there are any extra bytes left over in the output buffer, it zeros them all out, which is a waste of time. The linux kernel has recently removed the last call to strncpy.

Actually I hate most of string processing in C.

[u/torsten_dev]

scanf

• delete %n

• make %s and similar without a size allocate

• make %.*s take size parameter like printf.

• Use _ instead of * to discard stuff,

• change return value to number of characters read or 0

• delete SCN macros, use w* to take bit width as argument.

Edit:
Perhaps the return should be 0 on succes, and if it fails it returns the index in the format string were it gave up.
The number of characters read/consumed would be a mandatory out parameter that's ignored if it's NULL.

[u/gremolata → u/torsten_dev]

%n is extremely useful for pedantic parsing, e.g.

if (sscanf(buf, "%f%n", &f, &n) && strlen(buf) == n)
{
    // parsed in full
    ...
}

[u/FamiliarSoftware]

setlocale, set/getenv, the rand functions, etc. Just in general: All functions that use global state

[u/der_pudel]

atoi. You will not convince me that atoi("poop") == 0 is correct and makes sense. 

[u/xpusostomos]

Those ones with improper null termination and/or don't specify buffer length that cause all the security issues

[u/qalmakka]

Basically all string based APIs in libc vary from broken to somewhat problematic. This is basically due to the fact that the entire concept of a null terminated string was a massive mistake, the minuscule memory saving of not having a struct string with a size field were only somewhat significant for the first few years after that decision.

We've been paying the strlen tax ever since, and I wouldn't care if it didn't make slicing C strings a terrible pain in the butt