Data commit

Task/Stack/C/stack-2.c

@@ -0,0 +1,71 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stddef.h>
+#include <stdbool.h>
+
+#define check_pointer(p) if (!p) {puts("Out of memory."); exit(EXIT_FAILURE);}
+
+#define MINIMUM_SIZE 1
+ /* Minimal stack size (expressed in number of elements) for which
+ space is allocated. It should be at least 1. */
+#define GROWTH_FACTOR 2
+ /* How much more memory is allocated each time a stack grows
+ out of its allocated segment. */
+typedef int T;
+ // The type of the stack elements.
+
+typedef struct
+ {T *bottom;
+  T *top;
+  T *allocated_top;} stack;
+
+stack * new(void)
+/* Creates a new stack. */
+ {stack *s = malloc(sizeof(stack));
+  check_pointer(s);
+  s->bottom = malloc(MINIMUM_SIZE * sizeof(T));
+  check_pointer(s->bottom);
+  s->top = s->bottom - 1;
+  s->allocated_top = s->bottom + MINIMUM_SIZE - 1;
+  return s;}
+
+void destroy(stack *s)
+/* Frees all the memory used for a stack. */
+ {free(s->bottom);
+  free(s);}
+
+bool empty(stack *s)
+/* Returns true iff there are no elements on the stack. This
+is different from the stack not having enough memory reserved
+for even one element, which case is never allowed to arise. */
+ {return s->top < s->bottom ? true : false;}
+
+void push(stack *s, T x)
+/* Puts a new element on the stack, enlarging the latter's
+memory allowance if necessary. */
+ {if (s->top == s->allocated_top)
+     {ptrdiff_t qtty = s->top - s->bottom + 1;
+      ptrdiff_t new_qtty = GROWTH_FACTOR * qtty;
+      s->bottom = realloc(s->bottom, new_qtty * sizeof(T));
+      check_pointer(s->bottom);
+      s->top = s->bottom + qtty - 1;
+      s->allocated_top = s->bottom + new_qtty - 1;}
+  *(++s->top) = x;}
+
+T pop(stack *s)
+/* Removes and returns the topmost element. The result of popping
+an empty stack is undefined. */
+ {return *(s->top--);}
+
+void compress(stack *s)
+/* Frees any memory the stack isn't actually using. The
+allocated portion still isn't allowed to shrink smaller than
+MINIMUM_SIZE. If all the stack's memory is in use, nothing
+happens. */
+ {if (s->top == s->allocated_top) return;
+  ptrdiff_t qtty = s->top - s->bottom + 1;
+  if (qtty < MINIMUM_SIZE) qtty = MINIMUM_SIZE;
+  size_t new_size = qtty * sizeof(T);
+  s->bottom = realloc(s->bottom, new_size);
+  check_pointer(s->bottom);
+  s->allocated_top = s->bottom + qtty - 1;}