Re: [PATCH 1/5] Make xstrndup common

Hi,

On Sun, 29 Apr 2007, Josh Triplett wrote:

Daniel Barkalow wrote:

quoted

On Sat, 28 Apr 2007, Josh Triplett wrote:

quoted

Daniel Barkalow wrote:

quoted

It was implemented in commit.c; move it with the other x memory functions.

[...]

quoted

+static inline char *xstrndup(const char *str, int len)
+{
+	char *ret = xmalloc(len + 1);
+	memcpy(ret, str, len);
+	ret[len] = '\0';
+	return ret;
+}
+

I don't know if it matters, but this definition of xstrndup, like the 
version in commit.c, doesn't match the definition of strndup.  
strndup duplicates a string, copying up to n characters or the length 
of the string.  This xstrndup always copies n characters, reading 
past the end of the string if it doesn't have at least n characters.

Good catch. Replacing the memcpy with strncpy solves this, right? 
(Potentially allocating a bit of extra memory if someone is actually 
using it on too short a string for some reason, of course).

That would work, but it seems bad to allocate excess memory.  How about 
just using strlen and setting len to that if shorter, before doing the 
xmalloc and memcpy?  Yes, that makes two passes over the string, but I 
don't see any way around that.

Unless I am missing something, I think this should work:

static inline char *xstrndup(const char *str, int len)
{
	char *result = strndup(str, len);
	if (result == NULL)
		die ("xstrndup(): out of memory");
	return result;
}

Hmm?

Ciao,
Dscho

P.S.: If you feel real paranoid about it, you might insert

	if (result == NULL) {
		release_pack_memory(len, -1);
		result = strndup(str, len);
	}

before the if (...), but I think that's overkill.