Thread: Help with 2D arrays in C

i'm not sure how make 2d array in c.

code:

#include <stdlib.h>    void init_matrix(float*** matrix, int w, int h)  {  	int x, y;  	float** tmpmatrix = (float**)malloc(sizeof(float*) * h);  	  	if( tmpmatrix == null ) {  		printf("couldn't allocate memory grid, got null pointer.\n");  		exit(0);  	}  	  	for( y = 0; y < h; y++ ) {  		/* allocate row. */  		float* row = (float*)malloc(sizeof(float) * w);  		  		if( row == null ) {  			printf("couldn't allocate memory row (%d), got null pointer.\n", y);  			exit(0);  		}  		  		for( x = 0; x < w; x++ ) {  			row[x] = (y * w) + x;  		}  		  		/* store row. */  		printf("y = %d\n", y);  		tmpmatrix[y] = &row;  	}  	  	matrix = &tmpmatrix;  }    int main(int argc, char *argv[])  {  	/* initialize matrix. */  	float** matrix;  	int w = 512, h = 512, x = 0, y = 0;  	init_matrix(&matrix, w, h);  	  	/* test matrix. */  	for( y = 0; y < h; y++ ) {  		for( x = 0; x < w; x++ ) {  			printf("trying access %d,%d (y,x)\n", y, x);  			printf("answer=%d\n", matrix[y][x]);  		}  	}  }

the code segfaults... i'm not pointers 'point' (no pun intended) me in right direction?

php code:

#include <stdio.h>
#include <stdlib.h>

float **create_matrix(int w, int h)
{
    int i;
    float **matrix;
    
    matrix = (float **)calloc(h, sizeof(float *));
    if(matrix == null)
    {
        fprintf(stderr, "not enough memory!\n");
        exit(1);
    }
    
    for(i = 0; i < h; i++)
    {
        matrix[i] = calloc(w, sizeof(float));
        if(matrix[i] == null)
        {
            fprintf(stderr, "not enough memory!\n");
            exit(1);
        }
    }
    
    return matrix;
}

int main(int argc, char *argv[])
{
    int i, j, h = 9, w = 7;
    float **test = create_matrix(w, h);

    for(i = 0; i < h; i++)
        for(j = 0; j < w; j++)
            fprintf(stdout, "matrix[%d][%d] = %f\n", i, j, test[i][j]);

    return 0;
} 


here simpler , easier understand method. note calloc fills newly created memory 0 there no need _init_ array.

Forum The Ubuntu Forum Community Ubuntu Specialised Support Development & Programming Programming Talk Help with 2D arrays in C

Ubuntu