Simple memcpy Implementation Segfaults

Question

I am doing work for and OS class and for some reason bcc needs a memcpy even though I haven't called it in the code and its unavailable, so I'm rolling my own, however it keeps segfaulting `

void memcpy( void* destination, void* source, size_t bytes )
{
        size_t i = 0;
        char* destination__ = ( char* ) destination;
        char* source__ = ( char* ) source;
        if( !( destination__ == source__ ) )
        {
                for( ; i < bytes; ++i )
                        destination__[ i ] = source__[ i ];
        }
}

It seems to segfault and I am not sure why, it does fine when things are malloced but not for something like the following.

`

char* foo = "Hello";
char* bar = "Goodbye";
memcpy( bar, foo, 5 );

I have a feeling this is because foo and bar are likely global data, and it has something to do with that but Im not sure. I wouldent be asking except for the fact that I have found other implementations that are the same/similar online elsewhere. It crashes when compiled with regular ol' gcc which Im using to validate outside the OS Im building that has no diagnostics. Im confused as to why this is happening.

Does it still segfault if you declare your strings as `char[]` rather than `char*`? I think the problem is that those strings have been put in memory that's read only. And I think this is a duplicate, but I haven't yet found the original — Tim Randall, Dec 27 '18 at 19:38
@xing Will standardized implementations of memcpy crash when this happens? Due to Time Randall's insight I will close the question if it does. — The Floating Brain, Dec 27 '18 at 19:40
@TheFloatingBrain It isn't your `memcpy` implementation that's broken, but your test code. — Tim Randall, Dec 27 '18 at 19:42
Behavior of your test driver is undefined. You can't modify string literals. — SergeyA, Dec 27 '18 at 19:44
Grazie everyone, I just tested the standard memcpy in this case and it segfaults as well. Thank you all for your help. — The Floating Brain, Dec 27 '18 at 19:47

Simple memcpy Implementation Segfaults

0 Answers0