Question

I have a struct defined as

struct _element;
typedef struct _element Element;

struct _element {

    char* StudentName;
    char* StudentID;
    int StudentMarks;
};

A pointer to an Element struct is declared globally as

Element * ePtr;

Now I have a function that returns a pointer to an Element struct. This is defined as shown below. The same ePtr which was declared globally is populated in this function and then returned.

Element * CreateElement(char * jName, char * jID, int jMarks)
{
    printf("CreateElement \n");
    puts(jName); puts(jID); printf("%d\n",jMarks);

    ePtr->StudentName = (char*)malloc(sizeof(char)*strlen(jName));

    strcpy(ePtr->StudentName, jName);

    printf("After Creation \n");
    puts(ePtr->StudentName);

    return ePtr;
}

I am calling this function using

ePtr = CreateElement(iName,iID,iMarks);

from another function. The values stored in the parameters are correct, as shown by puts and printf commands just below the function call line.

My problem is that I’m getting a segmentation fault at the

ePtr->StudentName = (char*)malloc(sizeof(char)*strlen(jName));

line. I checked the same using gdb.

Answer 1

Are you allocating any memory for ePtr?

Just declaring a pointer to this struct globally isn’t enough: you’ll need to malloc some memory for it also: ePtr = malloc(sizeof(Element);.

Also be sure to add an extra slot in the malloc for your strings for the null terminator.

Generally, always initialize your pointers to NULL – you can do that when you declare the global: Element *ePtr = NULL;. Furthermore, try to get your ePtr out of the global-scope, and, check for NULL before you use a pointer, as with ePtr in your CreateElement method.