Assertion failure :: malloc - malloc

Question

I am running code in a coding site and got following error:
solution: malloc.c:2369: sysmalloc: Assertion `(old_top == (((mbinptr) (((char *) &((av)->bins[((1) - 1) * 2])) - __builtin_offsetof (struct malloc_chunk, fd)))) && old_size == 0) || ((unsigned long) (old_size) >= (unsigned long)((((__builtin_offsetof (struct malloc_chunk, fd_nextsize))+((2 * (sizeof(size_t))) - 1)) & ~((2 * (sizeof(size_t))) - 1))) && ((old_top)->size & 0x1) && ((unsigned long)old_end & pagemask) == 0)' failed.
Aborted (core dumped)
Code:
#include <stdio.h>
#include <string.h>
#include <math.h>
typedef struct cell
{
int x;
int y;
struct cell *prevcell;
struct cell *nextcell;
}cell;
/* Head ends here */
void nextMove(int x, int y, int pacman_x, int pacman_y, int food_x, int food_y, char grid[x][y]){
//logic here
int i=pacman_x;
int j=pacman_y;
cell *top,*node;
top = NULL;
while(grid[i][j] != '.')
{
node = NULL;
//UP
if(i != 0 && grid[i-1][j] != '%')
{
if(grid[i][j] != 'd')
{
printf("%d %d\n",i,j);
grid[i][j]='d';
}
//push
node = (cell*)malloc(sizeof(node));
node->x=i;
node->y=j;
node->prevcell=top;
node->nextcell=NULL;
if(top != NULL)
top->nextcell=node;
top=node;
i=i-1;
}
//LEFT
else if(j != 0 && grid[i][j-1] != '%')
{
if(grid[i][j] != 'd')
{
printf("%d %d\n",i,j);
grid[i][j]='d';
}
//push
node = (cell*)malloc(sizeof(node));
node->x=i;
node->y=j;
node->prevcell=top;
node->nextcell=NULL;
if(top != NULL)
top->nextcell=node;
top=node;
j=j-1;
}
//RIGHT
else if(j != y-1 && grid[i][j+1] != '%')
{
if(grid[i][j] != 'd')
{
printf("%d %d\n",i,j);
grid[i][j]='d';
}
//push
node = (cell*)malloc(sizeof(node));
node->x=i;
node->y=j;
node->prevcell=top;
node->nextcell=NULL;
if(top != NULL)
top->nextcell=node;
top=node;
j=j+1;
}
//DOWN
else if(i != x-1 && grid[i+1][j] != '%')
{
if(grid[i][j] != 'd')
{
printf("%d %d\n",i,j);
grid[i][j]='d';
}
//push
node = (cell*)malloc(sizeof(node));
node->x=i;
node->y=j;
node->prevcell=top;
node->nextcell=NULL;
if(top != NULL)
top->nextcell=node;
top=node;
i=i+1;
}
else
{
//pop
top=top->prevcell;
free(top->nextcell);
i=top->x;
j=top->y;
}
}
}
/* Tail starts here */
int main() {
int x, y;
int pacman_x, pacman_y;
int food_x, food_y;
scanf( "%d %d", &pacman_x, &pacman_y);
scanf( "%d %d", &food_x, &food_y);
scanf( "%d %d", &x, &y);
char grid[x][y];
for( int i=0; i<x; i++) {
scanf("%s[^\\n]%*c", grid[i]);
}
nextMove( x, y, pacman_x, pacman_y, food_x, food_y, grid);
return 0;
}
I am not getting the issue. Could someone help??

Answer 1

Your scanf() format is wrong.
scanf("%s[^\\n]%*c", grid[i]);
This is saying to scanf() for
1) a string (%s)
2) the character '['
3) the character '^'
4) the character '\'
5) the character 'n'
6) the character ']'
7) a char (%*c), but do not store it
You might want to drop the 's'
scanf("%[^\\n]%*c", grid[i]);
Idea:
char buf[80];
fgets(buf, sizeof(buf)-1, stdin);
sscanf(buf, "%[^\\n]", grid[i]);
I find it safer to separate Input from parsing.
Further, you have
char grid[x][y];
This appears to be a dynamically allocation of "grid" based on the size of x & y. This is not C (unless it a new feature). So I need to ask, what compiler are you using?

Answer 2

Ohh.. I got the issue.
The following malloc call is incorrect:
node = (cell*)malloc(sizeof(node));
It will allocate only 4 bytes (node being a pointer).
The correct version would be:
node = (cell*)malloc(sizeof(*node));
OR
node = (cell*)malloc(sizeof(cell));
How silly of me..!!