CODEWITHSUNDEEP
cpointersstructsegmentation-faultallocation
C Redmond
C Redmond

Reputation: 41

Getting a segmentation fault while reading from file

I am dealing with structures and char pointers (strings). I want to make an an array of structures and those structures have a char*, and two ints.

I am getting a segmentation fault when attempting to fscanf into the array and structs.

Here is the relevant part of my code.

Struct Def

typedef struct {
    char* title;
    int gross;
    int year;
} Movie;

Function I am heaving issues with

Movie* createArray(char *filename, int size)
{

    FILE *f;
    f = fopen(filename, "r");
    Movie* arr = (Movie*) malloc(sizeof(Movie) * size);
    if(!arr){printf("\nAllocation Failed\n"); exit(1);}
    for (int i =0; i<size; i++){
        fscanf(f, "%s %d %d", (arr+ i)->title, &arr[i].gross, &arr[i].year);
    }
    fclose(f);
    return arr;

}

To add on to that in case it is needed here is how I call the function

        Movie* arr = createArray(file1, records);

Upvotes: 2

Views: 83

Answers (1)

anastaciu
anastaciu

Reputation: 23822

title is an uninitialized pointer, you will also need to reserve memory for it, or simply declare title as a char array with desired size if that's an option.

There some other issues I felt like addressing in your function, some of them you might be aware of, code below with comments.

Movie* createArray(char *filename, int size)
{
    FILE *f;

    if(!(f = fopen(filename, "r"))){ //also check for file opening
        perror("File not found");
        exit(EXIT_FAILURE); //or return NULL and handle it on the caller
     }  

    //don't cast malloc, #include <stdlib.h>, using the dereferenced pointer in sizeof
    //is a trick commonly  used to avoid future problems if the type needs to be changed
    Movie* arr = malloc(sizeof(*arr) * size);    

    if(!arr) {
        perror("Allocation Failed"); //perror is used to output the error signature
        exit(EXIT_FAILURE);
    }

    for (int i =0; i<size; i++) {
        if(!((arr + i)->title = malloc(100))){ // 99 chars plus null terminator, 
            perror("Allocation failed");       // needs to be freed before the array
            exit(EXIT_FAILURE);   //using EXIT_FAILURE macro is more portable 
        }

        //always check fscanf return, and use %99s specifier 
        //for 100 chars container to avoid overflow
        if(fscanf(f, "%99s %d %d", (arr+ i)->title, &arr[i].gross, &arr[i].year) != 3){ 
            exit(EXIT_FAILURE); //or return NULL and handle it on the caller
        }
    }
    fclose(f);
    return arr;
}

Upvotes: 2

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