动态分配QImage数组

Question

I need to allocate dynamically memory for QImage array.

It worked for me in Linux:

void Arrange_Images(int numOfCams, int numBoards)
{
     QImage * array_of_images[numOfCams*numOfBoards];
     .
     .
     .
 }

But Windows will not resolve this problem and will mark it as error. For a standard array i can use malloc, but this is a QImage array. After this each cell will be filled by images for reordering and further processing. Thanks for help.

Answer 1

I think Visual Studio compiler still cannot allocate dynamic amount of memory on stack (I think C++03 didn't allowed this, altrough C99 did). You could use _malloca as an analogue. Or just switch to using gcc on Windows.

Answer 2

The problem is that your dynamic array is not really dynamic.

array_of_images is a static array of pointers to QImage objects, and the size of static arrays has to be known at compile time - this size is not known in your case since the size of your array depends on the input parameters of the Arrange_Images() function.

If you want to create a dynamically allocated array of QImage objects, you should do this this way:

QImage* array_of_images = new QImage[numOfCams*numOfBoards];

I would also consider if you really need a dynamically allocated array and cannot replace it with something like std::vector.

If the Linux compiler really allowed it in this form, I'm not sure why as it seems to me that it shouldn't compile.

Answer 3

To get it working quickly, try this line instead of what you have now:

std::vector<QImage*> array_of_images(numOfCams*numOfBoards);

You will need #include <vector> too, of course. Rest of your code should stay identical, as std::vector will unallocate itself (but not the stuff the pointers in it point to!) when it goes out of scope, just like your current C-style array does.