Thread: Pointers + Malloc = Painloc

1) Mem should be inside main.
2) You should initialize them to NULL unless you allocate some more memory.
3) The ending } should most likely be on its own line to help readability.
4) You must free what you malloc. You currently are not.

And just for the sake of it...
T* vs T *: http://www.research.att.com/~bs/bs_faq2.html#whitespace
If you're interested.

Originally Posted by Elysia

1) Mem should be inside main.
2) You should initialize them to NULL unless you allocate some more memory.
3) The ending } should most likely be on its own line to help readability.
4) You must free what you malloc. You currently are not.

And just for the sake of it...
T* vs T *: http://www.research.att.com/~bs/bs_faq2.html#whitespace
If you're interested.

There's nothing about the subject at the link you posted.

What *is* the difference?

Originally Posted by IceDane

There's nothing about the subject at the link you posted.
What *is* the difference?

There is a difference, in the way it's written and interpreted.
To the compiler, it's the same.

ok, I've gotten mem properly malloced, but I don't really understand what this is pointing to. *mem is pointing to a block of memory 256 bytes long, right? How do I put something in that memory? I.E., if I want the 245th byte to hold the hex "4a", how do I do that?

I've tried:

Code:

  void *mem = malloc(256); // I think this is the right initialization
  mem[245] = 71;
  *mem[245] = 71;
  (&mem)[245] = (void *)71;  // gives warning without cast
  mem += 245;  // increments by 245*4 bytes.  I think?
  *mem = 71;

none of them work, and in fact all lines (except for those with comments) above give a warning and an error:
warning: derefrencing 'void *' pointer
error: invalid use of void expression


What is a valid use of a void expression?


Edit: Elysia, I am freeing 'mem', I just didn't put it in the above code. I was typing it in a hurry.
EDIT 2: Maybe I found my answer? Does this make sense to anyone:

Code:

  void *mem = malloc(256);
  int i = 0;
  unsigned char *test;
  for(i=0; i<256; i++) {
    test = mem;
    if(i==0) *test = 71;
    printf("&#37;p(%p), ", (mem)++, *test);