Hi,

I am wrapping some C++ code for my personal project (opencvd), and I am creating so many array pointers at cpp side and containing them in structs. I want to learn if I am leaking memory like crazy, although I am not facing crashes so far. Is GC of D handling things for me? Here is an example:

```
//declaration in d
struct IntVector {
    int* val;
    int length;
}

// in cpp
typedef struct IntVector {
    int* val;
    int length;
} IntVector;

// cpp function returning a struct containing an array pointer allocated with "new" op.
IntVector Subdiv2D_GetLeadingEdgeList(Subdiv2D sd){
    std::vector<int> iv;
    sd->getLeadingEdgeList(iv);

    int *cintv = new int[iv.size()]; // I don't call delete anywhere?

    for(size_t i=0; i < iv.size(); i++){
        cintv[i] = iv[i];
    }
    IntVector ret = {cintv, (int)iv.size()};
    return ret;
};

// call extern c function in d:
extern (C) IntVector Subdiv2D_GetLeadingEdgeList(Subdiv2d sd);

int[] getLeadingEdgeList(){
    IntVector intv = Subdiv2D_GetLeadingEdgeList(this);
    int[] ret = intv.val[0..intv.length]; // just D magic. Still no delete anywhere!
    return ret;
}
```

The question is now: what will happen to "int *cintv" which is allocated with new operator in cpp code? I have many code similar in the project, but I have not encounter any problem so far even in looped video processings. Is GC of D doing deallocation automagically?
https://github.com/aferust/opencvd

On Saturday, 27 April 2019 at 22:25:58 UTC, Ferhat Kurtulmuş wrote:
> Hi,
>
> I am wrapping some C++ code for my personal project (opencvd), and I am creating so many array pointers at cpp side and containing them in structs. I want to learn if I am leaking memory like crazy, although I am not facing crashes so far. Is GC of D handling things for me? Here is an example:
>
> [...]
>
> The question is now: what will happen to "int *cintv" which is allocated with new operator in cpp code? I have many code similar in the project, but I have not encounter any problem so far even in looped video processings. Is GC of D doing deallocation automagically?
> https://github.com/aferust/opencvd

D's GC only collects memory allocated with D's `new` operator. Memory allocated by C++'s `new` operator must be freed by C++'s `delete` operator.

On Sunday, 28 April 2019 at 03:54:17 UTC, Paul Backus wrote:
> On Saturday, 27 April 2019 at 22:25:58 UTC, Ferhat Kurtulmuş wrote:
>> Hi,
>>
>> I am wrapping some C++ code for my personal project (opencvd), and I am creating so many array pointers at cpp side and containing them in structs. I want to learn if I am leaking memory like crazy, although I am not facing crashes so far. Is GC of D handling things for me? Here is an example:
>>
>> [...]
>>
>> The question is now: what will happen to "int *cintv" which is allocated with new operator in cpp code? I have many code similar in the project, but I have not encounter any problem so far even in looped video processings. Is GC of D doing deallocation automagically?
>> https://github.com/aferust/opencvd
>
> D's GC only collects memory allocated with D's `new` operator. Memory allocated by C++'s `new` operator must be freed by C++'s `delete` operator.

You are right. I am rewriting the things using mallocs, and will use core.stdc.stdlib.free on d side. I am not sure if I can use core.stdc.stdlib.free to destroy arrays allocated with new op.

On Sunday, 28 April 2019 at 23:10:24 UTC, Ferhat Kurtulmuş wrote:
> You are right. I am rewriting the things using mallocs, and will use core.stdc.stdlib.free on d side. I am not sure if I can use core.stdc.stdlib.free to destroy arrays allocated with new op.

core.stdc.stdlib.free is (as the name suggests) the standard C `free` function. As such, it can only be used to free memory allocated by the standard C functions `malloc`, `calloc`, and `realloc`. This is the same in D as it is in C and C++.

On Monday, 29 April 2019 at 00:53:34 UTC, Paul Backus wrote:
> On Sunday, 28 April 2019 at 23:10:24 UTC, Ferhat Kurtulmuş wrote:
>> You are right. I am rewriting the things using mallocs, and will use core.stdc.stdlib.free on d side. I am not sure if I can use core.stdc.stdlib.free to destroy arrays allocated with new op.
>
> core.stdc.stdlib.free is (as the name suggests) the standard C `free` function. As such, it can only be used to free memory allocated by the standard C functions `malloc`, `calloc`, and `realloc`. This is the same in D as it is in C and C++.

Thank you. It is now like:

/* c/cpp side */
extern (C) void deleteArr(void* arr);

void deleteArr(void* arr){
    delete[] arr;
}

struct IntVector Subdiv2D_GetLeadingEdgeList(Subdiv2D sd){
    std::vector<int> iv;
    sd->getLeadingEdgeList(iv);
    int *cintv = new int[iv.size()];
    for(size_t i=0; i < iv.size(); i++){
        cintv[i] = iv[i];
    }
    IntVector ret = {cintv, (int)iv.size()};
    return ret;
};

/* c/cpp side */

...
int[] getLeadingEdgeList(){ // d function
    IntVector intv = Subdiv2D_GetLeadingEdgeList(this);
    int[] ret = intv.val[0..intv.length].dup;
    deleteArr(intv.val);
    return ret;
}
...

On Saturday, 27 April 2019 at 22:25:58 UTC, Ferhat Kurtulmuş wrote:
> Hi,
>
> I am wrapping some C++ code for my personal project (opencvd), and I am creating so many array pointers at cpp side and containing them in structs. I want to learn if I am leaking memory like crazy, although I am not facing crashes so far. Is GC of D handling things for me? Here is an example:
>
> ```
> //declaration in d
> struct IntVector {
>     int* val;
>     int length;
> }
>
> // in cpp
> typedef struct IntVector {
>     int* val;
>     int length;
> } IntVector;
>
> // cpp function returning a struct containing an array pointer allocated with "new" op.
> IntVector Subdiv2D_GetLeadingEdgeList(Subdiv2D sd){
>     std::vector<int> iv;
>     sd->getLeadingEdgeList(iv);
>
>     int *cintv = new int[iv.size()]; // I don't call delete anywhere?
>
>     for(size_t i=0; i < iv.size(); i++){
>         cintv[i] = iv[i];
>     }
>     IntVector ret = {cintv, (int)iv.size()};
>     return ret;
> };
>
> // call extern c function in d:
> extern (C) IntVector Subdiv2D_GetLeadingEdgeList(Subdiv2d sd);
>
> int[] getLeadingEdgeList(){
>     IntVector intv = Subdiv2D_GetLeadingEdgeList(this);
>     int[] ret = intv.val[0..intv.length]; // just D magic. Still no delete anywhere!
>     return ret;
> }
> ```
>
> The question is now: what will happen to "int *cintv" which is allocated with new operator in cpp code? I have many code similar in the project, but I have not encounter any problem so far even in looped video processings. Is GC of D doing deallocation automagically?
> https://github.com/aferust/opencvd

Hello Ferhat,

You can use RCArray!T or Slice!(RCI!T) [1, 2] as common thread safe @nogc types for D and C++ code.
See also integration C++ example [3] and C++ headers [4].


RCArray (fixed length)
[1] http://mir-algorithm.libmir.org/mir_rc_array.html
RCSlice (allows to get subslices)
[2] http://mir-algorithm.libmir.org/mir_ndslice_allocation.html#rcslice
C++ integration example
[3] https://github.com/libmir/mir-algorithm/tree/master/cpp_example
C++ headers
[4] https://github.com/libmir/mir-algorithm/tree/master/include/mir

On Monday, 29 April 2019 at 14:38:54 UTC, 9il wrote:
> On Saturday, 27 April 2019 at 22:25:58 UTC, Ferhat Kurtulmuş wrote:
>> [...]
>
> Hello Ferhat,
>
> You can use RCArray!T or Slice!(RCI!T) [1, 2] as common thread safe @nogc types for D and C++ code.
> See also integration C++ example [3] and C++ headers [4].
>
>
> RCArray (fixed length)
> [1] http://mir-algorithm.libmir.org/mir_rc_array.html
> RCSlice (allows to get subslices)
> [2] http://mir-algorithm.libmir.org/mir_ndslice_allocation.html#rcslice
> C++ integration example
> [3] https://github.com/libmir/mir-algorithm/tree/master/cpp_example
> C++ headers
> [4] https://github.com/libmir/mir-algorithm/tree/master/include/mir
An opencv d binding using ndslice substituting cv::Mat would be useful like opencv-python using numpy. However, I started opencvd about a month ago, and I am very new to d. For now, I am the only contributor with zero mir.ndslice experience. When I gain more experience with ndslice, I would try it as substitution for cv::Mat. Thank you for links 9il. I will take a look at them.