C System Calls and messages

Question

I am trying to pass a pointer to a system call by passing a message with that call.

The pointer should be to an int[].

However the message definition expects a char pointer to be passed. How can I send an int pointer?

int pidarray[j];
m.m1_p1 = pidarray;

Is it possible to convert the pointer types?

Are you thinking of [syscalls(2)](http://man7.org/linux/man-pages/man2/syscalls.2.html) or of the [system(3)](http://man7.org/linux/man-pages/man3/system.3.html) library function when mentioning "C System Calls"? Please edit your question to improve it. Perhaps tag it more precisely (with Linux, POSIX, ...) — Basile Starynkevitch, Dec 03 '15 at 11:08

Michiel Pater · Answer 1 · 2015-12-03T10:57:06.787

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Is it possible to convert the pointer types?

Yes this is possible. e.g.:

(char*) intPointer

edited Dec 03 '15 at 10:57

answered Dec 03 '15 at 10:49

Michiel Pater

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Shouldn't it be `(char*)`? And wouldn't such a cast return the single bytes from each `int` instead of casting each `int` to a `char`? – cadaniluk Dec 03 '15 at 10:50
Thanks! How would that work in terms of passing it in the message? Do I convert it to a char*? Then I could pass it back as an int*? – calmcalmuncle Dec 03 '15 at 10:52
@cad I gave an example. And yes, the data would be directly converted to chars instead of per int. – Michiel Pater Dec 03 '15 at 10:54
Alright but casting something called `intPointer` to, well, an `int` pointer seems peculiar nevertheless. – cadaniluk Dec 03 '15 at 10:56
@calmcalmuncle Keep in mind that chars are 1 byte and integers are 4 bytes. – Michiel Pater Dec 03 '15 at 10:56
Thankyou for your answers! – calmcalmuncle Dec 03 '15 at 10:57
[Don't say that!](http://stackoverflow.com/questions/11438794/is-the-size-of-c-int-2-bytes-or-4-bytes) – cadaniluk Dec 03 '15 at 11:01

1 Answers1