Dynamic Memory Allocation :: malloc(3), calloc(3), bzero(3), memset(3)

Dynamic Memory Allocation :: malloc(3), calloc(3), bzero(3), memset(3)

• The prototype for malloc(3) is:

    void *malloc(size_t size);
  

  malloc takes in a size_t and returns a void pointer. Why does it return a void pointer? Because it doesn't matter to malloc to what type this memory will be used for.
• Let's see an example of how malloc is used:

    int *ip;
  
   ip = malloc(5 * sizeof(int));
   /* .. OR .. */
   ip = malloc(5 * sizeof(ip));
  

  Pretty simplistic. sizeof(int) returns the sizeof an integer on the machine, multiply by 5 and malloc that many bytes. The second malloc works because it sends what ip is pointing to, which is an int.
• Wait... we're forgetting something. AH! We didn't check for return values. Here's some modified code:

    #define INITIAL_ARRAY_SIZE 5
   /* ... code ... */
   int *ip;
  
   if ((ip = malloc(INITIAL_ARRAY_SIZE * sizeof(int))) == NULL) {
     (void)fprintf(stderr, "ERROR: Malloc failed");
     (void)exit(EXIT_FAILURE);    /* or return EXIT_FAILURE; */
   }
  

  Now our program properly prints an error message and exits gracefully if malloc fails.
• calloc(3) works like malloc, but initializes the memory to zero if possible. The prototype is:

    void *calloc(size_t nmemb, size_t size);
  

  Refer to Weiss pg. 164 for more information on calloc.
• bzero(3) fills the first n bytes of the pointer to zero. Prototype:

    void bzero(void *s, size_t n);
  

  If you need to set the value to some other value (or just as a general alternative to bzero), you can use memset:

    void *memset(void *s, int c, size_t n);
  

  where you can specify c as the value to fill for n bytes of pointer s.