Struggling using malloc and memcpy for dynamic mem allocation

malloc allocates a block of uninitialized, contiguous memory of the requested size in bytes and passes back a void* pointer since it has no idea what you want that memory for.

So, how do we calculate how many bytes we need then? Well, in this instance we have an array of characters, so we need space for each element (char) and the overall string size. To get the size of the element, we can use sizeof(char). To get the overall array size, we can use strlen(name) + 1.

This is your code:

(char*)malloc(strlen(name)) //If name is "apple", strlen will return 5 (it doesn't include the termination character '\0'). See: http://www.cplusplus.com/reference/cstring/strlen/

You see the issue? If you put a breakpoint at the printf line and look at the lunches[2] structure you'll see the name followed by random garbage because there isn't a null-termination character. This is why we need that +1 on both the malloc and memcpy to allocate space for the string terminator and to copy it, respectively.

Also you're getting lucky that the size of a char is a single byte, otherwise your malloc wouldn't allocate the correct size. Generally speaking, you want to get in the habit of doing it like malloc(sizeof(char) * (strlen(name) + 1)). It will lead to less headaches down the road (a char isn't always 1 byte). The "+1" won't be needed, for example, with an integer array though - malloc(sizeof(int) * arraySize).

This has nothing to do with your memory access problem though. That is caused by

free(name);
name = NULL;

You only free what you malloc. name is stack-allocated. It will be discarded when the stack-frame is popped on function exit. This is also why the line name = NULL; should show an error in your compiler. You can't re-assign name. It isn't a pointer to a char array, it is the char array. Did you mean to free the structure's name but accidentally referenced the local name instead?

 #define LUNCH_QTY 3
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(void)
{
   struct Food
   {
      char* name; int weight, calories;
   } lunches[LUNCH_QTY] = {{(char*)"apple", 4, 100}, {(char*)"salad", 2, 80}};

   for (int element = 2; element <= (LUNCH_QTY); element++)
   {
      char name[100];
      printf("Please enter, space-separated, the name, weight and calories of a food: ");
      if (scanf("%99s %d %d", name, &lunches[element].weight, &lunches[element].calories) == 1)
      {
         lunches[element].name = (char*)malloc(strlen(name)+1);
         if (lunches[element].name)
         {
            memcpy(lunches[element].name, &name, strlen(name)+1);
         }
         else
         {
            fputs("Unable to allocate memory\n", stderr);
            exit(1);
         }
      }
      else
      {
         fputs("Unable to read input\n", stderr);
         exit(1);
      }

      printf("%s %d %d", lunches[element].name, lunches[element].weight, lunches[element].weight);
      free(lunches[element].name);
      lunches[element].name = NULL;
   }
}