I'm new to c language and I have an assignment to allocate a dymanic matrix inside a function, put values in it and return to main and then call to another function that prints the matrix. I know that if I want to change the matrix values inside a function I need to use '&'. But when I return to main in order to print the matrix I get "Segmentation fault (core dumped)". Can somone tell me what's wrong with my code:
#include <stdio.h>
#include <stdlib.h>
int checkSize(int); //checking matrix size
void printMatrix(int **, int); //print matrix
int createMatrix(int ***, int); //allocate matrix and puts values from user.
int main()
{
int c; int **p=NULL;
printf("enter size of a matrix\n");
c=getchar();
if (checkSize(c))
{
if((createMatrix(&p, c-'0'))!=0)
printMatrix(p, c-'0');
}
return 0;
}
int checkSize(int c)
{
if (c>'9'||c<'0')
return 0;
return 1;
}
int createMatrix(int ***p, int n)
{
int m=n;
int k;
p=(int***)malloc(m*sizeof(int**));
for (k=0; k<m; k++)
p[k]=(int**)malloc(m*sizeof(int*));
printf("enter numbers\n");
int *l;
int i;
int c;
for (i=0; i<m; i++)
{
k=n;
for (l=(int*)(p)+i;k>0;l++)
{
c=getchar();
if (c==EOF)
{
printf("error EOF");
return 0;
}
if (c>'9'||c<'0')
{
printf("error");
return 0;
}
*l=c-'0';
k--;
}
}
return 1;
}
void printMatrix(int **p, int n)
{
int k=n;
int* l;
int i;
int m=n;
for (i=0; i<k; i++)
{
m=n;
printf("\n");
for (l=(int*)(p)+i;m>0;l++)
{
printf("%d ", *l);
m--;
}
}
}
One issue is your memory allocation. You allocate space for the wrong types and save the result incorrectly. That is
p=(int***)malloc(m*sizeof(int**));
should be
*p = malloc(m * sizeof(int*));
and
p[k]=(int**)malloc(m*sizeof(int*));
should be
(*p)[k] = malloc(m * sizeof(int));
Here is an alternative approach that doesn't operate directly on the input argument:
#include <stdio.h>
#include <stdlib.h>
int create(int ***m, int n)
{
int i, j;
// Create the matrix
int** p = malloc(n * sizeof *p); // ToDo: Check return value
for (i=0; i < n; ++i)
{
p[i] = malloc(n * sizeof **p); // ToDo: Check return value
}
for (i=0; i < n; ++i)
{
for (j=0; j < n; ++j)
{
*(p[i] + j) = 10 * i + j;
}
}
// Assign the matrix to the passed pointer
*m = p;
return 0;
}
void pm(int **m, int n)
{
int i, j;
for (i=0; i < n; ++i)
{
for (j=0; j < n; ++j)
{
printf("%d ", *(m[i] + j));
}
printf("\n");
}
}
int main(void) {
int** m;
create(&m, 5);
pm(m, 5);
// ToDo: Add code to free memory
return 0;
}
Output:
0 1 2 3 4
10 11 12 13 14
20 21 22 23 24
30 31 32 33 34
40 41 42 43 44
note For clarity check of malloc
return value is omitted.