xmemdup0

[Eric Blake]

Would anyone else be interested in adding xmemdup0 to the xalloc module?  In 
m4, I have several places where I copy blocks of arbitrary memory, but want to 
guarantee that it is NUL-terminated so that I can later do things like 
comparing strlen(ptr) with the length to check for the (relatively rare) case 
of embedded NULs in that block of memory.  Another use case for guaranteeing 
the terminating NUL is in algorithms such as replacing backslash escape 
sequences in regex replacement blocks (since the gnulib regex module can 
already handle embedded NUL transparently).  It's more efficient to detect an 
unterminated escape sequence at the end of a block if you can always read the 
byte after a backslash, and only on seeing NUL decide whether the sequence was 
invalid or the string exhausted, compared to having to check if the memory 
block has been exhausted yet for every backslash prior to reading the next byte.

/* Allocate N + 1 bytes, copy N bytes from PTR, and NUL-terminate the result.
   Call xalloc_die on failure.
   In C++, the return type matches PTR, with any const removed.  */
void *
xmemdup0 (void const *ptr, size_t n)
{
  void *result = memcpy (xmalloc (n + 1), ptr, n);
  result[n] = 0;
  return result;
}

-- 
Eric Blake