CODEWITHSUNDEEP
cmultidimensional-arraystructure
rayapati ramya
rayapati ramya

Reputation: 5

finding the size of a multidimensional array?

#include<stdio.h>
#include<stdlib.h>
#include<stdint.h>
struct Array {
    uint32_t* row;
};


int main()
{
    
    struct Array* a = malloc(sizeof(struct Array) * 2);
    
    a[0].row = malloc(sizeof(uint32_t) * 3);
    a[1].row = malloc(sizeof(uint32_t) * 2);
    
    uint32_t temp1[] =  {2,3,4};
    uint32_t temp2[] = {5,8};
    
    
    for(int i=0;i<3;i++)
    a[0].row[i] = temp1[i];
    
    for(int i=0;i<2;i++)
    a[1].row[i]= temp2[i];

    for(int i=0;i<2;i++)
    {
        int len = sizeof(a[i].row)/sizeof(a[i].row[0]);
        for(int j=0;j<len;j++)
        {
            printf("%d\t",a[i].row[j]);
        }
        printf("\n");
    }
}

I have a multidimensional array. rows in the array can be of different size so i used a structure.

Now I want to print the elements in the array. But its not printing in the right way.

2   3   
5   8

This is showing as my output.

int len = sizeof(a[i].row)/sizeof(a[i].row[0]);

I think there is something wrong in the above line. please help me to print the elements of array correctly

Upvotes: 0

Views: 92

Answers (1)

0___________
0___________

Reputation: 67476

It will not work this way as it will give you the size of the pointer in uint32_t units.

If you want to dynamically allocate the 2D array you need to keep the sizes somewhere in your data. Here is an example (access using array pointer):

typedef struct
{
    size_t cols, rows;
    uint32_t data[];
}Array2D;

Array2D *alloc2DArray(const size_t rows, const size_t cols)
{
    return malloc(rows * cols * sizeof(uint32_t) + sizeof(Array2D));
}

void printArray(const Array2D *arr)
{
    uint32_t (*array)[arr -> cols] = (uint32_t (*)[])arr -> data;

    for(size_t row = 0; row < arr -> rows; row++)
    {
        for(size_t col = 0; col < arr -> cols; col++)
            printf("%"PRIu32" ", array[row][col]);
        printf("\n");
    }
}

Sizes are kept in the struct and the actual data in the flexible struct member.

Remember to use the correct type to store the sizes (size_t)

Upvotes: 1

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