How to reallocate content on bigger storage but that the rest of content be zero?

Question

How to reallocate content on bigger storage but that the rest of content be zero ? I have at the moment like

void* oldContent;
size_t oldContentSize;
size_t newBufferSize;

realloc(oldContent, newBufferSize);

How to achieve that all with inde from oldContentSize to the end of new buffer have value '\0' ?

Your question has been asked before: http://stackoverflow.com/questions/2141277/how-to-zero-out-new-memory-after-realloc — dcaswell, Sep 04 '13 at 20:14
If you are on a Windows platform, you can use HeapAlloc/HeapReAlloc instead. Passing the HEAP_ZERO_MEMORY flag will zero the end of the new buffer. — josh poley, Sep 04 '13 at 20:20

score 1 · Accepted Answer · answered Sep 04 '13 at 20:15

1

void*newContent;
newContent = realloc(oldContent,newBufferSize);
memset(newContent + oldContentSize, 0, newBufferSize - oldContentSize);

answered Sep 04 '13 at 20:15

geocar

This won't compile. Can't do arithmetic on a void pointer. – Lee Daniel Crocker Sep 04 '13 at 20:17
@LeeDanielCrocker: gcc permits `void*` arithmetic as an extension (with the unpleasant side effect that `sizeof (void) == 1`). Use one of the `-std=` options to warn about it. – Keith Thompson Sep 04 '13 at 22:39

score 1 · Answer 2 · answered Sep 04 '13 at 20:16

1

Just have to do it yourself:

oldContent = realloc(oldContent, newBufferSize);
memset((char *)oldContent + oldBufferSize, 0, newBufferSize-oldBufferSize);

answered Sep 04 '13 at 20:16

Don't forget to check that `oldContent != NULL` before calling `memset`. And if `realloc` fails, you've just lost your old pointer value (which may be ok if you're not going to need it again). – Keith Thompson Sep 04 '13 at 22:40

2 Answers2