CODEWITHSUNDEEP
csegmentation-fault
Ayro
Ayro

Reputation: 42

C - Segmentation fault(core dumped)

I am making a Rubik's Cube that can rotate it's rows and columns. My struct is this:

typedef struct
{
int **cell;
}face;

In this part I am allocating memory for cells. (X is user input)

face faceOne; //There are six of this faces
faceOne.cell = (int **)malloc(x * sizeof(int));
for(int i = 0; i < x; i++)
     faceOne.cell[i] = (int *)malloc(x * sizeof(int));

Then I am filling these cells:

for (int i = 0; i <  x; i++)
  for (int j = 0; j < x; j++)
     {
     faceOne.cell[i][j] = 0;
     printf("%d\n", i);
     }

If x is bigger than 3, program crashes with Segmentation fault. How can i solve this?

Upvotes: 0

Views: 83

Answers (2)

user2736738
user2736738

Reputation: 30936

faceOne.cell = (int **)malloc(x * sizeof(int));

would be

faceOne.cell = malloc(x * sizeof(int*));

Otherwise you are allocating memory for x int variables and then storing int* variable on it. In case sizeof(int) = sizeof(int*) then it wont be any problem but on the system where this is not the case you have earned yoruself a undefined behavior.

To get rid of all this ** while using malloc the best would be to do this

faceOne.cell = malloc(x * sizeof *faceOne.cell);

Similarly,

faceOne.cell[i] = malloc(x * sizeof *faceOne.cell[i] );

And also don't cast the return value of malloc. This suppresses many warning generated by compiler and is unnecessary.

Apart from all this, have you ever wondered what would happen if malloc did fail and returned NULL? Then you are working on a NULL and dereferencing it(Undefined behavior). Check the return value of malloc, in case it returns NULL handle the error and move on.

Upvotes: 2

D&#233;j&#224; vu
D&#233;j&#224; vu

Reputation: 28850

You want here

faceOne.cell = (int **)malloc(x * sizeof(int));

to allocate x pointers to int, so this should be

faceOne.cell = malloc(x * sizeof(int *));

It seems on your system the size of a pointer (to int) is bigger than the size of an int ...

Also in C don't cast malloc() (see this)

Upvotes: 0

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