Added pop and made empty's return make more sense.

src/dyn_arr.c

@@ -3,6 +3,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+
 #define ARRAY_GROWTH_MULTIPLIER 1.3
 
 void *dyn_arr_init(size_t item_size, size_t capacity) {
@@ -19,13 +20,6 @@ void *dyn_arr_init(size_t item_size, size_t capacity) {
   return dyna_ptr;
 }
 
-bool dyna_empty(void *array) {
-  if (dyna_length(array) == 0) {
-    return false;
-  }
-  return true;
-}
-
 void *dyna_ensure_capacity(void *array, size_t item_count, size_t item_size) {
   dyna_header *header = dyna_get_header(array);
   size_t minimum_capacity = header->length + item_count;
@@ -44,3 +38,31 @@ void *dyna_ensure_capacity(void *array, size_t item_count, size_t item_size) {
   header->capacity = new_capacity;
   return header + 1;
 }
+
+void dyn_arr_pop(void *array, size_t item_size) {
+  if (dyna_empty(array)) {
+    return;
+  }
+
+  dyna_length(array)--;
+
+  // Shrink if smaller than growth factor, may break if growth factor is > 2
+  if (dyna_length(array) >
+      (2 - ARRAY_GROWTH_MULTIPLIER) * dyna_capacity(array)) {
+    return;
+  }
+
+  size_t new_capacity = dyna_length(array) * ARRAY_GROWTH_MULTIPLIER;
+  dyna_capacity(array) = new_capacity;
+
+  size_t new_size = sizeof(dyna_header) + new_capacity * item_size;
+  dyna_header *header = dyna_get_header(array);
+  header = realloc(dyna_get_header(array), new_size);
+}
+
+bool dyna_empty(void *array) {
+  if (dyna_length(array) == 0) {
+    return true;
+  }
+  return false;
+}

src/dyn_arr.h

@@ -1,7 +1,7 @@
 #pragma once
 
-#include <stdlib.h>
 #include <stdbool.h>
+#include <stdlib.h>
 
 #define ARRAY_INITIAL_CAPACITY 4
 
@@ -10,13 +10,16 @@
  * - Capacity
  *   - shrink capacity to size
  * - Modifiers
- *   - clear
+ *   - clear aka erase
  *   - insert
  *   - (optional) insert range
  *   - pop
  *   - (optional) swap
  *   - (optional) resize
-*/
+ * - Sanity checks
+ *   - Check data going into array is the right size
+ *   - see if possible to check entered data is correct type
+ */
 
 typedef struct dyna_header {
   size_t capacity;
@@ -27,14 +30,19 @@ typedef struct dyna_header {
 #define dyna_init(T) (T *)dyn_arr_init(sizeof(T), ARRAY_INITIAL_CAPACITY)
 void *dyn_arr_init(size_t item_size, size_t capacity);
 
+// Modification
 #define dyna_append(array, value)                                              \
   ((array) = dyna_ensure_capacity(array, 1, sizeof(value)),                    \
    (array)[dyna_get_header(array)->length] = (value),                          \
    &(array)[dyna_get_header(array)->length++])
 
+void *dyna_ensure_capacity(void *array, size_t item_count, size_t item_size);
+
+#define dyna_pop(array) dyn_arr_pop(array, sizeof(typeof(*array)))
+void dyn_arr_pop(void *array, size_t item_size);
+
 // Get meta data
 #define dyna_get_header(array) ((dyna_header *)(array)-1)
 #define dyna_length(array) (dyna_get_header(array)->length)
 #define dyna_capacity(array) (dyna_get_header(array)->capacity)
-bool dyna_empty(void* array);
+bool dyna_empty(void *array);
-void *dyna_ensure_capacity(void *array, size_t item_count, size_t item_size);

src/main.c

@@ -1,16 +1,20 @@
 #include "dyn_arr.h"
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 
 int main() {
-  int *dyna_array = dyna_init(int);
+  uint64_t *dyna_array = dyna_init(uint64_t);
-  printf("empty %d\n", dyna_empty(dyna_array));
 
-  for (int i = 0; i < 999999999; i++) {
+  for (uint64_t i = 0; i < 9999999; i++) {
     dyna_append(dyna_array, i);
   }
-  printf("capacity %zu\n", dyna_capacity(dyna_array));
+
-  printf("empty %d\n", dyna_empty(dyna_array));
+  for (uint64_t i = 9999999; i > 0; i--) {
+    printf("length: %zu capacity: %zu\n", dyna_array[i],
+           dyna_capacity(dyna_array));
+    dyna_pop(dyna_array);
+  }
 
   return EXIT_SUCCESS;
 }