How to send a dynamically created array as a parameter to a function?

Question

How to send a dynamically created array as a parameter to a function?

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#1 by (2 votes)

2

In the exec I am developing, I try to pass a dynamically created array created with the malloc function, but doing so compiles the pointer type as incompatible.

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

void substituiNegativos(int c, int mat[][c]){

    int i, j;

    for(i=0; i< 2; i++){
        for(j=0; j< 2; j++){

            if(mat[i][j] < 0){
                mat[i][j] = abs(mat[i][j]);
            }
        }
    }

    for(i=0; i< 2; i++){
        for(j=0; j<2; j++){

            printf("%d ", mat[i][j]);
        }
        printf("\n");
    }
}

int main()
{

    int i, j, l, c;

    printf("Numero de linhas: ");
    scanf("%d", &l);

    printf("Numero de colunas: ");
    scanf("%d", &c);

    int **mat = (int**)malloc(l * sizeof(int));

    for(i=0; i<l; i++){

        mat[i] = (int*)malloc(c * sizeof(int));

        for(j=0; j<c; j++){

            printf("Insira o numero: ");
            scanf("%d", &mat[i][j]);
        }
    }

    substituiNegativos(c, mat);

    return 0;
}

c malloc

asked by anonymous 28.02.2018 / 21:25

1 answer

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score 2 · Accepted Answer

In C, in the function argument, you need to tell the compiler how many columns you have in your array, due to the fact that the array is nothing more than a vector, but with a rows and columns logic, for example:

int main()
{
    int matriz[3][3] = {10,20,30,40,50,60,70,80,90};
    int i, j;

    for(i=0;i<3;i++)
    {
        for(j=0;j<3;j++)
        {
            printf("%d ", matriz[i][j]);
        }
        printf("\n");
    }
}

The result will be this:

Matriz[i][j] -> 10 20 30 40 50 60 70 80 90
         [i] -> 0  0  0  1  1  1  2  2  2
         [j] -> 1  2  3  1  2  3  1  2  3

The compiler needs to know that for such a row it has a grouping of X memory locations (columns) with values, so it requires you to declare at least the number of columns. To solve your problem, you can declare a quantity of columns. Example:

void substituiNegativos(int c, int mat[][100])

Or, declare a vector pointer. Example:

void substituiNegativos(int c, int *mat[])

Either one will work.