Comment by dobin
2 years ago
Imho its pretty simple: Strings in C are 0-terminated char arrays. If the char array is not 0-terminated, its not a string.
strncpy() can make a string into a non-string (depending on size), which is clearly bad.
2 years ago
Imho its pretty simple: Strings in C are 0-terminated char arrays. If the char array is not 0-terminated, its not a string.
strncpy() can make a string into a non-string (depending on size), which is clearly bad.
That’s because strncpy does not return a nul-terminated (“C”) strings, but a fixed-size nul-padded strings.
That, as it turns out, is the case of most (but not all) strn* functions.
Of course strncpy adds the injury that it’s specified to alllow nul-terminated inputs (it stops at the first nul byte, before filling the target buffer with nuls).
It also, in some situations, returns a *string" that doesn't have the null terminator, which means it is giving the caller something that literally isn't a string.
It always “returns” the same thing: a fixed size nul-padded buffer. Call it a char array if you want, that’s always been it’s role and contract.
> Strings in C are 0-terminated char arrays
To be pedantic, they're pointers to char. Nothing more. Calling them array confuses non-C coders. The length is just an unenforced contract and has to be passed.
It's a pointer to a chunk of memory which contains an array of characters. You pass around the pointer because copying an array is expensive and wasteful.
I think (or hope) the concepts are pretty clear if you understand what a pointer is.
strncpy was a bad mistake. If you know the length and there's no null termination, you use memcpy instead.
strncpy isn't good either. But using length delimited strings is the best way to generate fixed length char strings and NUL terminated strings.