Return Struct from Function in C

Question

I'm very new to langage C and I need to make a lot of matrix calculation and I decided to use a matrix struct.

Matrix.h

struct Matrix
{
    unsigned int nbreColumns;
    unsigned int nbreRows;
    double** matrix;
};

struct Matrix CreateNewMatrix(unsigned int n,unsigned int m);
double GetMatrixValue(struct Matrix* m,unsigned int ligne,unsigned int colonne);

Matrix.c

#include "matrix.h"

struct Matrix CreateNewMatrix(unsigned int n,unsigned int m){
    struct Matrix mat;
    mat.nbreColumns = n;
    mat.nbreRows = m;
    mat.matrix = (double**)malloc(n * sizeof(double*));

    unsigned int i;
    for(i = 0; i < n; i++)
    {
        mat.matrix[i] = (double*)calloc(m,sizeof(double));
    }

    return mat;
}

double GetMatrixValue(struct Matrix* m,unsigned int ligne,unsigned int colonne){
    return m->matrix[ligne][colonne];
}

Then I compile, no errors ...

I made a few tests :

Main.c

struct Matrix* m1 = CreateNewMatrix(2,2);

printf("Valeur : %f",GetMatrixValue(m1,1,1));

Edit : When I run my code, I had ".exe has stop working" ..

What did i do wrong ?

".exe has stop working" Did you get an exception thrown ? If yes, what is it ? — Gabriel L.
– Gabriel L., Commented Nov 5, 2013 at 18:37

Charlie Burns · Accepted Answer · 2013-11-05 18:37:34Z

2

CreateNewMatrix returns a Matrix not a Matrix*

struct Matrix* m1 = CreateNewMatrix(2,2);
printf("Valeur : %f",GetMatrixValue(m1,1,1));

should be

struct Matrix m1 = CreateNewMatrix(2,2);
printf("Valeur : %f",GetMatrixValue(&m1,1,1));

You should compile with all warnings on and not run the program until all the warnings go away.

answered Nov 5, 2013 at 18:37

Charlie Burns

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Comments

Adam · Accepted Answer · 2013-11-05 18:37:25Z

0

You declare CreateNewMatrix to return a struct:

struct Matrix CreateNewMatrix(unsigned int n,unsigned int m){

But when you use it you expect a pointer to a struct:

struct Matrix* m1 = CreateNewMatrix(2,2);

This should be a compiler error, though.

answered Nov 5, 2013 at 18:37

Adam

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1 Comment

John smith Over a year ago

I don't why but i changed the return of CreateNewMatrix from a struct to pointer and it's now working fine ! Thanks

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