Invalid Write with strcpy - c

Question

I have been programming for a while but I am new to C. I have this linked list implementation in ansi C that I need to test. I have narrowed the problem down to an issue with an invalid write. I ran the code through Valgrind and received the following output:
==18131== Invalid write of size 1
==18131== at 0x4C2C0CC: __GI_strcpy (in /usr/lib/valgrind/vgpreload_memcheck-amd64 linux.so)
==18131== by 0x40089B: main (in /home/btm7984/hw3/TestList)
==18131== Address 0x51f1388 is 0 bytes after a block of size 8 alloc'd
==18131== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==18131== by 0x400880: main (in /home/btm7984/hw3/TestList)
==18131==
==18131== Invalid write of size 1
==18131== at 0x4C2C0DF: __GI_strcpy (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==18131== by 0x40089B: main (in /home/btm7984/hw3/TestList)
==18131== Address 0x51f138e is 6 bytes after a block of size 8 alloc'd
==18131== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==18131== by 0x400880: main (in /home/btm7984/hw3/TestList)
==18131==
--18131-- VALGRIND INTERNAL ERROR: Valgrind received a signal 11 (SIGSEGV) - exiting
--18131-- si_code=1; Faulting address: 0x6D4FCAA; sp: 0x402bdae00
All that I can ascertain from this is that I am allocating something wrong. I think it has to be with my strcpy line. I really don't know how to approach this question. What follows is my use of the LinkedLists interface. InitLinkedLists, AddToBackOfList, and DestroyList are all defined in that interface.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "LinkedLists.h"
int main(int argc, char *argv[]) {
FILE *fp;
char tmpString[100];
LinkedLists *ListPtr = malloc(sizeof(LinkedLists));
ElementStructs *DataPtr;
LinkedListNodes* curr = malloc(sizeof(LinkedListNodes));
int counter = 0;
int Done = 0;
InitLinkedList(ListPtr);
fp = fopen(argv[1], "r");
if (!fp){
fprintf(stderr,"%s Cannot open file %s\n", argv[0], argv[1]);
exit(1);
}
do{
fscanf(fp,"%s",tmpString);
if (!feof(fp)) {
DataPtr = malloc(sizeof(DataPtr));
printf("%d %d : %d\n",counter,(int)strlen(DataPtr->str),(int)strlen(tmpString));
strcpy(DataPtr->str,tmpString);
DataPtr->index=counter;
AddToBackOfLinkedList(ListPtr, DataPtr);
counter++;
Done = 1;
} else {
Done = 0;
}
}while (Done);
In conclusion, I think strcpy is causing an invalid write and I don't know why.
Any help would be greatly appreciated. Thanks in advance.
EDIT: ElementStructs is defined as follows:
typedef struct ElementStructs
{
/* Application Specific Definitions */
int index;
char str[100];
} ElementStructs;

Answer 1

The problem resides in this statement:
DataPtr = malloc(sizeof(DataPtr));
You allocate only enough memory to hold a pointer and not a full struct.
You should allocate using:
DatapPtr = malloc(sizeof(ElementStructs));
or, as described in the comments (WhozCraig):
DatapPtr = malloc(sizeof(*DataPtr));