SAS/C Library Reference, Vol. 1

free -- Free a Block of Memory

SYNOPSIS

 #include <stdlib.h>

 void free(void *block);

DESCRIPTION

free frees a block of memory previously allocated by malloc or calloc. block is a pointer to the memory block.

RETURN VALUE

free has no return value.

ERRORS

User ABEND 1206, 1207, or 1208 may occur if memory management data areas are overlaid. User ABEND 1208 will probably occur if the block pointer is invalid; that is, if it does not address a previously allocated area of memory that has not already been freed.

IMPLEMENTATION

If an entire page of memory is unused after a free call, the page is returned to the operating system unless the page is included in the initial heap area whose size can be specified with a run-time argument.

EXAMPLE

  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>

  struct LIST
  {
     struct LIST *next;
     char text[0];  /* Zero-length arrays are a SAS/C extension. */
  };

  main(int argc, char *argv[])
  {
     struct LIST *p;
     struct LIST *q;
     struct LIST list;
     char str[256];
     int size;

     while (1){
        puts("nBegin new group...");
        for (q = &list; ; q = p){
           puts("Enter a text string: ");
           if (fgets(str,sizeof(str),stdin) == NULL){
              break;
           }
           if (str[0] == '0'){
              if (q == &list)
                 exit(EXIT_SUCCESS);
              break;
           }
           size = sizeof(struct LIST) + strlen(str) + 1;
           p = (struct LIST *)malloc(size);
           if (p == NULL){
              puts("No more memory");
              exit(EXIT_FAILURE);
           }
           q->next = p;
           p->next = NULL;
           strcpy(p->text, str);
        }

        puts("nnTEXT LIST...");

           /* Be sure to copy the next pointer from */
           /* the current block before you free it. */

        p = list.next;
        while(p != NULL){
           q = p->next;
           printf(p->text);
           free((char *)p);
           p = q;
        }
        list.next = NULL;

        exit(EXIT_SUCCESS);
     }
  }

RELATED FUNCTIONS

pfree