Function Returning Pointer to Struct Segmentation Fault

Question

I am working on a project that deals with a struct and has various functions that manipulate the given struct.

I have started off with my initial function that just allocates the memory for the struct, and initialises each item in the struct and then returns a pointer to the struct. I have already defined the struct in my header file. I then have a main file that I will eventually use to run all my functions, however I am having trouble just running this first one, it seg faults every time I run it.

header:

#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <limits.h>

struct Double_Array{
    double** array;
    int rowsize;
    int colsize;
};

struct Double_Array* double_array(int,int);

function:

#include "header.h"


struct Double_Array* double_array( int row, int col){

    int i;

    struct Double_Array* ptrDouble_Array;

    ptrDouble_Array = (struct Double_Array*) malloc(sizeof(struct Double_Array));

    ptrDouble_Array -> rowsize = row;

    ptrDouble_Array -> colsize = col;
    for(i=0;i< ptrDouble_Array -> colsize ; i++){
        ptrDouble_Array -> array[i] = malloc((sizeof(double))*(row));
    }
    return(ptrDouble_Array);
}

mainline:

#include "header.h"


int main(){
    srand(time(0));
    printf("running");
    int i;
    int j;
    struct Double_Array* ptr;

    ptr = double_array( 5, 5);

    for(i=0;i<5;i++){
        free(ptr->array[i]);
    }
    free(ptr);

    return(0);

}

I've spent a while looking for possible issues, but everything looks logically correct to me.

What is causing the Seg fault

dbush · Accepted Answer · 2020-02-07 05:08:31Z

3

You're allocating space for each array[i], but you never allocate space for array. So ptrDouble_Array->array[i] is dereferencing an uninitialized pointer, which causes the segfault.

Add the allocation:

ptrDouble_Array->array = malloc((sizeof(double *))*(col));
for(i=0;i< ptrDouble_Array->colsize ; i++){
    ptrDouble_Array->array[i] = malloc((sizeof(double))*(row));
}

And don't forget to free it:

for(i=0;i<5;i++){
    free(ptr->array[i]);
}
free(ptr->array);
free(ptr);

answered Feb 7, 2020 at 5:08

dbush

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