Re: Passing arrays to C funcions

From:

ds <junkmailavoid@yahoo.com>

Newsgroups:

comp.lang.c++

Date:

Tue, 04 Sep 2007 16:58:48 -0000

Message-ID:

<1188925128.006899.9660@d55g2000hsg.googlegroups.com>

On Sep 4, 6:51 pm, Erik Wikstr=F6m <Erik-wikst...@telia.com> wrote:

On 2007-09-04 18:21, ds wrote:

On Sep 4, 6:05 pm, red floyd <no.s...@here.dude> wrote:

ds wrote:

Hi all,

I have to pass an array of doubles to a legacy C function that copies
some data using memcpy. The code would look like this:

extern "C"{
void legacyCFunctionFill(void* arg);
}
...
int number=5;
double *my_array=(double*)calloc(number,sizeof(double));
legacyCFunctionFill((void*)my_array);
// Do sth useful
free(my_array);

The question is: if I change calloc() and free() with new and delete
[] will there be any issues, including portability issues? At first =

seems that it works, having tested that in my program. But I am not
sure if the memory allocated by calloc is the same and can be used t=

same way as the memory allocated with new, especially on windows,
Linux and Sun.

Assuming that legacyCFunctionFill() doesn't overrun the buffer (how
*does* it know how much space to fill?), it's fine to use
new[]/delete[]. A pointer is a pointer.

double *my_array = new double[number];
legacyCFunctionFill(my_array); // no cast to void* needed
delete[] my_array; // note use of delete[]

Alternatively:

std::vector<double> myvec(number);
legacyCFunctionFill(&myvec[0]);
// no deletion necessary

Hi floyd,

it is clear that number has to be passed to the legacy function, which
performs a memcpy - no allocation/deallocation on the passed array.
Are you sure that std::vector allocates a continuous block? That would
be a nice solution for what I want to do, but I am afraid that not
all std::vector implementations allocate continuous memory....

All standards compliant std::vectors allocate continuous blocks of memory.

--
Erik Wikstr=F6m

I agree. But are all stl implementations complying to the standard?
Especially the MSVC implementation deviates in some cases...