Comment by dmitrygr
Comment by dmitrygr 5 days ago
Lucky for us C programmers. Each distro provides its own trusted libc, and my code has no other dependencies. :)
Comment by dmitrygr 5 days ago
Lucky for us C programmers. Each distro provides its own trusted libc, and my code has no other dependencies. :)
C (actually POSIX) has a hashmap implementation: https://man7.org/linux/man-pages/man3/hsearch.3.html
What it doesn't have is a hashmap type, but in C types are cheap and are created on an ad-hoc basis. As long as it corresponds to the correct interface, you can declare the type anyway you like.
char *
left_pad (const char * string, unsigned int pad)
{
char tmp[strlen (string)+pad+1];
memset (tmp, ' ', pad);
strcpy (tmp+pad, string);
return strdup (tmp);
}
Not a C expert but you’re using a dynamic array right on the stack, and then returning the duplicate of that. Shouldn’t that be Malloc’ed instead?? Is it safe to return the duplicate of a stack allocated array, wouldn’t the copy be heap allocated anyway? Not to mention it blows the stack and you get segmentation fault?
> and then returning the duplicate of that. Shouldn’t that be Malloc’ed instead??
Like the sibling already wrote, that's what strdup does.
> Is it safe to return the duplicate of a stack allocated
Yeah sure, it's a copy.
> wouldn’t the copy be heap allocated anyway?
Yes. I wouldn't commit it like that, it is a naive implementation. But honestly I wouldn't commit leftpad at all, it doesn't sound like a sensible abstraction boundary to me.
> Not to mention it blows the stack and you get segmentation fault?
Yes and I already mentioned that in my comment.
---
> dynamic array right on the stack
Nitpick: It's a variable length array and it is auto allocated. Dynamic allocation refers to the heap or something similar, not already done by the compiler.
strdup allocates
strndup would be safer if I correctly recall from my C days?
Safer for what? That opinion seems to be misguided to me.
strndup prevents you from overrunning the allocation of a string given that you pass it the containing allocations size correctly. But if you got passed something that is not a string, there will be a buffer overrun right there in the first line. Also what outer allocation?
You use strcpy when you get a string and memcpy when you get an array of char. strncpy is for when you get something that is maybe a string, but also a limited array. There ARE use cases for it, but it isn't for safety.
Do you rewrite fundamental data structures over and over, like maps, of just not use them?