Crash on big array in C++

Question

I am working on OpenCL and I code like this in MS VS 2012:

cl_float test[480000];

It can be complied successfully but the program crashes when it enter the function which the codes above are in. Error Code: 0xC000041D.

It is interrupted near the end of file "chkstk.asm":

; Find next lower page and probe
cs20:
        sub     eax, _PAGESIZE_         ; decrease by PAGESIZE
        test    dword ptr [eax],eax     ; probe page.
        jmp     short cs10

_chkstk endp

        end

On the line test dword ptr [eax],eax ; probe page..

I don't think this array is too big to be allocated.

So next, I want to try another way:

cl_float4 *PixVectIn=(cl_float4*)malloc(480000*sizeof(cl_float4));
for(unsigned int a=0;a<800;a++){
    for(unsigned int b=0;b<600;b++){
        PixVectIn[a*800+b].x=PixVect[a][b][0];
        PixVectIn[a*800+b].y=PixVect[a][b][1];
        PixVectIn[a*800+b].z=PixVect[a][b][2];
    }
}

The program also can be built. This time, it crashes when run the "for" loop.

It stop at PixVectIn[a*800+b].x=PixVect[a][b][0];. It shows me the same error code and at this moment, a=600 and b=252. Looks like it reaches a boundary something.

I'm not sure. It may because I changed certain options in project properties.

For the first, 1MB is a typical stack size limit, and the array is larger than that. For the second, 600*800 + 252 is greater than 480000. — user253751, Nov 12 '15 at 07:44
[Is there a max array length limit in C++?](http://stackoverflow.com/a/216731/14065) — Martin York, Nov 12 '15 at 10:44

score 3 · Accepted Answer · answered Nov 12 '15 at 07:47

3

First you should compare the pointer malloc returned with NULL, otherwise you don't know if the allocation was successful.

Second your indices are wrong: PixVectIn[a*800+b] will go out of the bounds of 480000, since your a alone goes up to 800, and 800^2 is > 480000. Maybe you meant a*b?

answered Nov 12 '15 at 07:47

Superlokkus

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Probably meant a*600+b. – user253751 Nov 12 '15 at 07:58
Ok, I got it. I made a simple mistake. This is stupid... I want to do `PixVectIn[b*800+a]`. Thank you. – Soban Nov 12 '15 at 08:03

score 1 · Answer 2 · answered Nov 12 '15 at 07:52

1

Increase your stack size or declare that array as static or place it in global scope. Your stack (in your case) is not big enough to handle 1920000 bytes...

answered Nov 12 '15 at 07:52

Malkocoglu

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Even better, the array should be a (dynamically allocated) heap data. For example, by using `std::vector` – Basile Starynkevitch Nov 12 '15 at 07:55
@Basile: Your suggestion is good. I do not know if OpenCL can work with std:vector or similar. Any info ? – Malkocoglu Nov 12 '15 at 07:57
1

Read more about C++11 [std::vector](http://www.cplusplus.com/reference/vector/vector/). You can use its `data` member function to get a pointer. You might want to upgrade your compiler to something C++11 compliant – Basile Starynkevitch Nov 12 '15 at 08:01

score 1 · Answer 3 · answered Nov 12 '15 at 08:00

First program is bitten by stack overflow.

For the second, a*800+b is access violation for values like 799, 800*800 + 600 > 480000.

Also better replace this:

cl_float4 *PixVectIn=(cl_float4*)malloc(480000*sizeof(cl_float4));

with this:

std::vector<cl_float4> PixVectIn(480000);

Crash on big array in C++

3 Answers3