On Feb 5, 2:07 pm, Gianni Mariani <gi4nos...@mariani.ws> wrote:
> sam wrote:

> > I want to ask question about following:-
> > #define SIZE 6000
> > long ret=0x00001515;
> > char buf[SIZE+5];
> > *(long*)&buf[strlen(buf)]=ret;
> > what exactly happenning at the last line of code.

A programmer is proving himself incompetent?

> That is a type cast, dereference and assignment. Very
> non-portable code BTW - on some machines it will crash and on
> some it will arrange bytes differently.

Most importantly, here: the cast is a reinterpret_cast, which
always depends somewhat on the implementation. (Why the
original author chose to hide this critical information from us
by using a C style cast is another question.)

> Assuming that between the definition of buf and the last line, there is
> an initialization of buf taking place, what is happening is that it is
> placing at the end of the null terminated string in buf a long.

> e.g. if buf contained the sequence 'a', 'b', 'c', '\0', x, x, x, y then,
> assuming long is a 4 byte type, the nul and the locations marked as 'x'
> will be replaced with the contents of "ret" which could be 0x15, 0x15,
> 0, 0 -or- 0, 0, 0x15, 0x15 or some other machine dependant format of
> "long" (could be 64 bit or 16 bit, you jusy don't know).

Just a nit, but strlen() returns the length of the string
without the final '\0', so the final '\0' will be overwritten.
And long can't be 16 bits, since LONG_MAX must be at least
2147483647.

But those are just nits---as you say, you just don't know.

FWIW, on my machine, if buf is initialized with "abc" (e.g. by
string copy), the code crashes. (long is 8 bytes, and requires
8 byte alignment.)

--
James Kanze (GABI Software) email:james.kanze@gmail.com
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