I've tried to create a matrix in C and have some input value, but I don't know why it throws me a "segmentation error". This is my code:
#include <stdio.h>
#include <stdlib.h>
int main() {
int i;
int j;
int **a;
a = malloc(5 * sizeof(int));
for (i = 0; i < 5; i++) {
a[i] = malloc(4 * sizeof(int));
}
for (i = 0; i < 5; i++) {
for (j = 0; j < 4; j++) {
scanf("%d", (a[i][j]));
}
}
return 0;
}
Given the answer by @Bathsheba, this is what your code should look like:
#include <stdio.h>
#include <stdlib.h>
int main (void)
{
int (*a)[4] = malloc( sizeof(int[5][4]) );
for(int i=0;i<5;i++)
{
for(int j=0;j<4;j++)
{
scanf("%d", &a[i][j]);
}
}
free(a);
return 0;
}
void func (size_t x, size_t y, int array[x][y]). Where int array[x][y] will get adjusted by the compiler ("decay") into a pointer to the first element: int (*array)[y]. Which is exactly what we have in the caller.a should bea=malloc(5*sizeof(int*));
Note well the pointer type in the sizof. On some systems (Windows desktops in the early 2000s) an int just happened to be the same size as an int*, but you must not assume that.
scanf takes a pointer as the parameter: the clearest way to write this is scanf("%d", &a[i][j]);
Don't forget to free the memory once you're all done.
Finally, I die a little inside every time I see a matrix modelled like this. Granted, it allows you to use the [][] notation, but normally it's better to model it as a contiguous memory block and use the idiom i * columns + j to access the element at (i, j).
i * columns + j isn't necessary since 1999. One can use a pointer to a VLA and thereby get the convenient [][] syntax.
scanf("%d", &(a[i][j]));