Using memcpy() on a char **buffer

Question

If I have a pointer to a message buffer how do I memcpy() into that buffer? For example say I have the following:

char **buffer;
char data[10]

memcpy(*buffer, data, 10);

But this doesn't seem to work and always crashes my program, however the compiler doesn't see to mind. Can someone please tell me why? Btw the reason I have a char **buffer is because its being passed as a parameter of the function.

before writing memory, you need to allocate. also theres nothing to stop you passing a char * into a function.. — amdixon
– amdixon, Commented Nov 16, 2013 at 0:23
buffer points nowhere specified and *buffer points nowhere specified. Writing to the unknown is undefined behaviour. — Havenard
– Havenard, Commented Nov 16, 2013 at 0:25

David Heffernan · Accepted Answer · 2013-11-16 00:25:54Z

2

The pointer variable buffer does not point to anything. You need to allocate memory and make buffer point to it. For instance:

buffer = malloc(sizeof(*buffer));
*buffer = malloc(10);
memcpy(*buffer, data, 10);

answered Nov 16, 2013 at 0:25

David Heffernan

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