Passing a matrix in a function (C)

Question

I have an issue passing a matrix to a function in C. There is the function I want to create:

void ins (int *matrix, int row, int column);

but I noticed that in contrast to the vectors, matrix give me an error. How can I pass my matrix to a function so?

EDIT --> there is the code:

// Matrix

#include <stdio.h>
#define SIZE 100

void ins (int *matrix, int row, int column);
void print (int *matrix, int row, int column);

int main ()
{
    int mat[SIZE][SIZE];
    int row, col;

    printf("Input rows: ");
    scanf  ("%d", &row);
    printf("Input columns: ");
    scanf  ("%d", &col);

    printf ("Input data: \n");
    ins(mat, row, col);

    printf ("You entered: ");
    print(mat, row, col);

    return 0;
}

void ins (int *matrix, int row, int column);
{
    int i, j;

    for (i = 0; i < row; i++)
    {
        for (j = 0; j < column; j++)
        {
            printf ("Row %d column %d: ", i+1, j+1);
            scanf  ("%d", &matrix[i][j]);
        }
    }
}

void print (int *matrix, int row, int column)
{
    int i;
    int j;

    for(i=0; i<row; i++)
    {
        for(j=0; j<column; j++)
        {
            printf("%d ", matrix[i][j]);
        }
        printf("\n");
    }
}

How much are the diemensions of your matrix? Is it 1D or 2D? — , Jul 11 '12 at 08:34
Possible duplicate http://stackoverflow.com/questions/546860/passing-arrays-and-matrices-to-functions-as-pointers-and-pointers-to-pointers-in/11274267#11274267 — Ulterior, Jul 11 '12 at 08:40

score 37 · Accepted Answer · edited Oct 29 '20 at 02:37

37

You need to pass a pointer with as much levels of indirection (*) as the number of dimensions of your matrix.

For example, if your matrix is 2D (e.g. 10 by 100), then:

void ins (int **matrix, int row, int column);

If you have a fixed dimension (e.g. 100), you can also do:

void ins (int (*matrix)[100], int row, int column);

or in your case:

void ins (int (*matrix)[SIZE], int row, int column);

If both your dimensions are fixed:

void ins (int matrix[10][100], int row, int column);

or in your case:

void ins (int matrix[SIZE][SIZE], int row, int column);

edited Oct 29 '20 at 02:37

Marco Bonelli

63,369
21
118
128

answered Jul 11 '12 at 08:29

Thanks. If i have a constant dimension (look my edits) defined SIZE, how need do i change the code? – Lc0rE Jul 11 '12 at 08:38
2

It is not possible to pass a 2D array as in the OP's example through "a pointer with as much levels of indirection (*) as the number of dimensions of your matrix". That part of the answer is completely incorrect. – AnT stands with Russia Nov 14 '21 at 20:04

score 14 · Answer 2 · answered Jul 11 '12 at 09:10

If you have a modern C compiler you can do the following for 2D matrices of any sizes

void ins (size_t rows, size_t columns, int matrix[rows][columns]);

Important is that the sizes come before the matrix, such that they are known, there.

Inside your function you then can access the elements easily as matrix[i][j] and the compiler is doing all the index calculations for you.

score 2 · Answer 3 · answered Oct 10 '13 at 09:37

2

it would also possible to leave the first dimension empty, the same as (*matrix):

void ins (int matrix[][100], int row, int column);

answered Oct 10 '13 at 09:37

asam

359
3
12

score 0 · Answer 4 · edited Apr 26 '16 at 03:33

Much better way to use malloc function and create dynamically allocated array and do whatever you want to do using 2d array:

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

void fun(int **arr,int m,int n)
{
    int i, j;
    for (i = 0; i < m; i++)
    {
    for (j = 0; j < n; j++)
        {
            scanf("%d", &arr[i][j]);
        }
    }

}

int main()
{
    int i,j,m,n;
    printf("enter order of matrix(m*n)");
    scanf("%d*%d",&m,&n);
    int **a=(int **)malloc(m*sizeof(int));
    for(i=0;i<n;i++)
        a[i]=(int *)malloc(n*sizeof(int));

    fun(a,m,n);
    for (i = 0; i < m; i++)
    {
    for (j = 0; j < n; j++)
        {
        printf("%d ", a[i][j]);
        }
        printf("\n");

    }
    return 0;
}

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

void fun(int **arr,int m,int n)
{
    int i, j;
    for (i = 0; i < m; i++)
    {
    for (j = 0; j < n; j++)
        {
            scanf("%d", &arr[i][j]);
        }
    }

}

int main()
{
    int i,j,m,n;
    printf("enter order of matrix(m*n)");
    scanf("%d*%d",&m,&n);
    int **a=(int **)malloc(m*sizeof(int));
    for(i=0;i<n;i++)
        a[i]=(int *)malloc(n*sizeof(int));

    fun(a,m,n);
    for (i = 0; i < m; i++)
    {
    for (j = 0; j < n; j++)
        {
        printf("%d ", a[i][j]);
        }
        printf("\n");

    }
    return 0;
}

score -1 · Answer 5 · edited Dec 21 '21 at 14:50

-1

You can try this as well:

void inputmat(int r,int c,int arr[r * sizeof(int)][c * sizeof(int)])

edited Dec 21 '21 at 14:50

Tomerikoo

18,379
16
47
61

answered Dec 21 '21 at 14:42

Souvik Roy

1
1

Passing a matrix in a function (C)

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