创建结构的二维数组会导致崩溃

Question

I am trying to generate a two-dimensional array of a struct , but this results in the program not launching. The window freezes and the program quits after a few seconds. Any idea why?

This is the file where I try to define the array cells .

#ifndef _FIELD_H_
    #define _FIELD_H_

class Field {
    public:
        static const int minX = -400;
        static const int maxX = 400;
        static const int minY = 0;
        static const int maxY = 400;

        Field();

    private:
        struct absCell {
            int material;
            float health;
        } cells[maxX - minX + 1][maxY - minY + 1];
};

#endif

The program is able to run when I remove these four lines:

        struct absCell {
            int material;
            float health;
        } cells[maxX - minX + 1][maxY - minY + 1];

Any idea how this happens? Any help is appreciated!

Update

Okay, apparently the problem is that this array gets quite big. Maybe you can help me to optimize this.

Material has to be an int between 0 and 10. Health has to be a float between 0 and 1 with a maximum of 2 fractional digits.

How can I limit the size of these vars?

Update 2

Mark B suggested the use of vectors while itwasntpete suggested the use of pointers, new and delete. Where is the difference, what are the advantages and disadvantages of these two methods? Thanks again!

Answer 1

you are allocating 801 * 401 (=321201) elements of struct absCell on the stack. assuming you have a 32bit machine it is 2569608 Byte (~2.45 MB). this is blowing up your stack. see here .

move the elements to heap like:

class Field {
public:
    static const int minX = -400;
    static const int maxX = 400;
    static const int minY = 0;
    static const int maxY = 400;

    Field() {
        cells = new absCell*[maxX - minX + 1];
        for(int i=0; i<maxX - minX + 1; i++)
            cells[i] = new absCell[maxY - minY + 1];
    }

    ~Field() {
        for(int i=0; i<maxX - minX + 1; i++)
            delete[] cells[i];

        delete[] cells;
    }

private:
    struct absCell {
        unsigned char material;
        unsigned char health;
    }**cells;
};

should solve your problem.

since your update material and health can be saved in a char . accessing health you have to recalculate it:

put -> x*100
get -> x/100

and dont forget to cast it.

Answer 2

Based on update note:

The first thing you can do is easily optimize your struct for space by using unsigned char for each attribute, using a fixed-point representation for your existing float (for example 0.23 would be stored as the integer 23).

Then store the structs on the heap with vector instead of an array:

    struct absCell {
        unsigned char material;
        unsigned char health;
    };
    std::vector<std::vector<absCell> > cells_;

Then set up the constructor:

Field() : cells_(maxX - minX + 1, std::vector<absCell>(maxY - minY + 1)) {}

Answer 3

My guess is you're hitting the stack limit. When you make that array like it is its trying to put 801*401*8 bytes on your stack. I did a quick compile and was having crashes until I lowered the numbers for your various mins and maxes.

Answer 4

If I got your snippet right way, you're trying to create an array. Allocation of the array is stack-based, with more than 2 Mb size required. There may be a chance that your stack has less than that 2Mb available, thus the code crashes right at the moment you're entering the function.

Try to allocate the same array dinamically.