Thread: Returning a double matrix

Hi there,

Do you know how to make **myMatrix a double pointer? This is what I have done considering it an int pointer...

Code:

int **Matrix(int (*matrixSize)[2])
{
    (*matrixSize)[0]=3; // number of rows.
    (*matrixSize)[1]=5; // number of cols.
// These numbers are obtained from another function. 
// Not shown here, for the sake of simplicity.
// They are supposed to be 3 and 5, respectively.
    
    
// Allocating myMatrix (a two-dimensional array)...
    int **myMatrix;
    
    myMatrix=malloc((*matrixSize)[0]*sizeof(int*));
    
    if (myMatrix==NULL)
    {
fprintf(stderr, "Error: Out of memory\n");
        exit(-1);
    }
    
    for (int i=0; i<(*matrixSize)[0]; i++)
    {
        myMatrix[i]=malloc((*matrixSize)[1]*sizeof(int));
        
        if (myMatrix==NULL)
        {
fprintf(stderr, "Error: Out of memory\n");
            exit(-1);
        }
    }
    
// Filling myMatrix with numbers...
    for (int i=0; i<(*matrixSize)[0]; i++)
        for (int j=0; j<(*matrixSize)[1]; j++)
            myMatrix[i][j]=5*i-2*j;
    
    return &(myMatrix[0]);
}




int main (int argc, const char * argv[])
{
        int msize[2];
        
        int **m=Matrix(&msize);
        
        for (int i=0; i<msize[0]; i++)
            for (int j=0; j<msize[1]; j++)
                printf("m[%i][%i] = %i\n",i,j,m[i][j]);
    
    return 0;
}

Thank you very much for your kind of help.

Ricardo.

What have you tried? Does your int function work properly?

Jim

Dear quzah. Do you mean this?

Code:

int **Matrix(int (*matrixSize)[2]);
int **Matrix(int (*matrixSize)[2])
{
int numRows=3; // number of rows.
int numCols=5; // number of cols.
// These numbers are obtained from another function. 
// Not shown here, for the sake of simplicity.
// They are supposed to be 3 and 5, respectively.
    
    (*matrixSize)[0]=numRows;
    (*matrixSize)[1]=numCols;
    
// Allocating myMatrix (a two-dimensional array)...
    int **myMatrix;
    
    myMatrix=malloc(numRows*sizeof(int*));
    
    if (myMatrix==NULL)
    {
fprintf(stderr, "Error: Out of memory\n");
        exit(-1);
    }
    
    for (int i=0; i<numRows; i++)
    {
        myMatrix[i]=malloc(numCols*sizeof(int));
        
        if (myMatrix[i]==NULL)
        {
fprintf(stderr, "Error: Out of memory\n");
            exit(-1);
        }
    }
    
// Filling myMatrix with numbers...
    for (int i=0; i<numRows; i++)
        for (int j=0; j<numCols; j++)
            myMatrix[i][j]=5*i-2*j;
    
    return myMatrix;
}




int main (int argc, const char * argv[])
{
    //@autoreleasepool {
        int msize[2];
        
        int **m=Matrix(&msize);
        
        for (int i=0; i<msize[0]; i++)
            for (int j=0; j<msize[1]; j++)
                printf("m[%i][%i] = %i\n",i,j,m[i][j]);
    //}
    
    return 0;
}

What about making **myMatrix a double pointer?

Thank you!

Ok... I did it! Thank you Quzah.

Another question... to free memory, I need to do this, isn't it?

Code:

for (int i=0; i<msize[0]; i++) 
     free(m[i]);


free(m);

I mean,

Code:

#import <Foundation/Foundation.h>


double **Matrix(int (*matrixSize)[2]);
double **Matrix(int (*matrixSize)[2])
{
    int numRows=3; // number of rows.
    int numCols=5; // number of cols.
    // These numbers are obtained from another function. 
    // Not shown here, for the sake of simplicity.
    // They are supposed to be 3 and 5, respectively.
    
    (*matrixSize)[0]=numRows;
    (*matrixSize)[1]=numCols;
    
    // Allocating myMatrix (a two-dimensional array)...
    double **myMatrix;
    
    myMatrix=malloc(numRows*sizeof(double*));
    
    if (myMatrix==NULL)
    {
        fprintf(stderr, "Error: Out of memory\n");
        exit(-1);
    }
    
    for (int i=0; i<numRows; i++)
    {
        myMatrix[i]=malloc(numCols*sizeof(double));
        
        if (myMatrix[i]==NULL)
        {
            fprintf(stderr, "Error: Out of memory\n");
            exit(-1);
        }
    }
    
    // Filling myMatrix with numbers...
    for (int i=0; i<numRows; i++)
        for (int j=0; j<numCols; j++)
            myMatrix[i][j]=1/9.*i-2.*j;
    
    return myMatrix;
}




int main (int argc, const char * argv[])
{
    @autoreleasepool {
        int msize[2];
        
        double **m=Matrix(&msize);
        
        for (int i=0; i<msize[0]; i++)
            for (int j=0; j<msize[1]; j++)
                printf("m[%i][%i] = %f\n",i,j,m[i][j]);
        
        // Realeasing memory...
        for (int i=0; i<msize[0]; i++) 
            free(m[i]);
        
        free(m);
    }
    
    return 0;
}

Thank you!