Reading with fscanf segmentation fault

Question

I am currently trying to initialize a 2d array with values but keep encountering a segmentation fault...I noticed it always occurred when I added the fscanf line of code...but I don't understand what's wrong with it since from my understanding it should work...this is a code snippet:

    FILE * fp;
        int count, i,j;
        int **arr;

        arr = (int**)malloc(sizeof(int*)*9);
        for(i = 0; i < 9; i++){
            arr[i] = (int*)malloc(sizeof(int)*9);
        }    

fp = fopen("input.txt", "r");

    for(i = 0; i < 9; i++){
            for(j = 0; j < 9; j++){
                fscanf(fp, "%d", &arr[i][j]);
            }
        }

Standard Warning : Please [do not cast](http://stackoverflow.com/q/605845/2173917) the return value of `malloc()` and family in `C`. — Sourav Ghosh, Apr 28 '15 at 08:14
added the code snippet for fp...sorry must've missed it when I copied — user3580218, Apr 28 '15 at 08:17
I'm not too well-versed in C but based on what I know it fails if the file does not exist? I do have a file in the same directory named input.txt though — user3580218, Apr 28 '15 at 08:25
ok my mistake...it was failing because the name of the file is "input" not "input.txt". I should not have included the file extension — user3580218, Apr 28 '15 at 08:28

score 1 · Accepted Answer · answered Apr 28 '15 at 08:20

1

In your code, you neither

checked for the sucess of malloc()
checked for the success of fopen().

For any of the cases,

if malloc() fails, it will return NULL and using that pointer will cause undefined behaviour.
if fopen() fails, it will return NULL, and using the file pointer later will again cause undefined behaviour.

Put a chcek for sucess of all the library functions (in general) and use the return value only if they are successful.

answered Apr 28 '15 at 08:20

Sourav Ghosh

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apparently fp is showing up as null...though I do have a file on the same directory named input.txt – user3580218 Apr 28 '15 at 08:22
In the case of the 2d array I tried initializing the value of the 2d array I made and it did print out the values so it is not null...Also I just figured out that the name of the file was the problem...It should be "input" not "input.txt"...I did not need to add a file extension...my mistake sorry – user3580218 Apr 28 '15 at 08:31

Reading with fscanf segmentation fault

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