Large unexpected u16_t buf

Question

I have C function that calls pointer to function (with pointer to buf and size of buf)

printf("------------------------------\n");
printf("lengh of DATA_output = %zu\n", p->tot_len);
(*myStr.OnSendData)(buf, p->tot_len);
printf("------------------------------\n");

pointer to function defined like

typedef void (*pOnSendData)(void *buf, u16_t len);

Then my real c++ class method gets it through that pointer:

void Someclass::myPOnSendData(void *buf, u16_t len) {
std::cout << " Someclass::mypOnSendData len = " << (int)len << std::endl;
//Do something
}

The problem is that len of buf is pretty large.

output is :

------------------------------
lengh of DATA_output = 42
------------------------------

Someclass::myPOnSendData len = 50512

How could that be?

@ValentinMercier Over my head. What is C/C++, if not a language? — Fiddling Bits, Jul 28 '14 at 13:32
`void (*)(void *, size_t)` is incompatible with `void (*)(void *, u16_t)` — Drew McGowen, Jul 28 '14 at 13:32
@Fiddling, C and C++ are not the same language, and never were: from day one, there were valid C programs that could not be compiled by a C++ compiler, and obviously the other way around. — Frédéric Hamidi, Jul 28 '14 at 13:36
C/C++ is used cus there is a 'C' lib and I need C++ application. Is that a problem? Please, stop HOLY WARS. Help me with this thing.. please. — RedCollarPanda, Jul 28 '14 at 13:36
@FrédéricHamidi Oh, I see. ValentinMercier is saying C and C++ are not the same language. I thought he was saying C and C++ are not languages at all. Sorry. — Fiddling Bits, Jul 28 '14 at 13:37
@RedCollarPanda, maybe consider `[c-libraries]` for this purpose. Tried that for you. — Frédéric Hamidi, Jul 28 '14 at 13:38
@ValentinMercier C/C++ is not a language. They are two different languages, and this question is about interfacing between them. Your edit (which I reverted) completely changed the meaning. — interjay, Jul 28 '14 at 13:38
@ValentinMercier, sorry for my mistake - my brain is boiling... — RedCollarPanda, Jul 28 '14 at 13:42
you don't need to dereference a function pointer because it'll be done automatically http://stackoverflow.com/questions/24508504/function-pointer-why-is-fptr6-7-same-as-fptr6-7-if-the-function-is — phuclv, Jul 28 '14 at 13:47

score 0 · Accepted Answer · answered Jul 28 '14 at 13:44

You say that myPOnSendData is not a static member function, but you are trying to assign a pointer to it into a C pointer-to-function. This won't work because C-style pointers to functions do not support non-static member function.

If you change the function to be static, it will be compatible with the pointer type.

Note that since the types are currently incompatible, you probably got an error message when trying to assign the function pointer, and had to perform a cast to get around it. Don't do this, as you are just hiding the error rather than solving it.

Large unexpected u16_t buf

1 Answers1