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Comment by TheTxT

11 hours ago

But how do you left pad a string?

7 comments

TheTxT

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1718627440  8 hours ago 

    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);
    }

Doesn't sound too hard in my opinion. This only works for strings, that fit on the stack, so if you want to make it robust, you should check for the string size. It (like everything in C) can of course fail. Also it is a quite naive implementation, since it calculates the string size three times.

  • brabel  7 hours ago

    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?

    • 1718627440  7 hours ago

      > 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.