stack.c

@@ -8,8 +8,8 @@ StackNode *push(StackNode *stack, void *data)
     if(node == NULL)
         return stack; // allocation failed -> return unchanged stack
 
-    node->data = data;      // Setze Daten   
+    node->data = data;      // Set the data for the new node   
-    node->next = stack;     // Setze nächsten Knoten auf aktuellen Stack
+    node->next = stack;     // New node points to the previous top of the stack
     return node;
 }
 
@@ -21,7 +21,7 @@ StackNode *pop(StackNode *stack)
         return NULL;
 
     StackNode *next = stack->next;
-    // Speicher des aktuellen Knotens freigeben
+    // Do NOT free stack->data here; caller owns the pointed data
     free(stack);
     return next;
 }

test_stack.c

@@ -8,45 +8,37 @@ int main(void)
     StackNode *s = NULL;
 
     // push 3 integers
-    int *a = malloc(sizeof(int)); 
+    int *a = malloc(sizeof(int)); *a = 1; s = push(s, a);
-    *a = 1; 
+    int *b = malloc(sizeof(int)); *b = 2; s = push(s, b);
-    s = push(s, a);
+    int *c = malloc(sizeof(int)); *c = 3; s = push(s, c);
-    int *b = malloc(sizeof(int)); 
-    *b = 2; 
-    s = push(s, b);
-    int *c = malloc(sizeof(int)); 
-    *c = 3; 
-    s = push(s, c);
 
-    // oben liegt c (3)
+    // top should be c (3)
     int *topv = (int *)top(s);
     if(topv == NULL || *topv != 3) { fprintf(stderr, "stack top expected 3\n"); return 1; }
 
-    // oben liegt nun 2
+    // pop -> now top should be 2
     s = pop(s);
     topv = (int *)top(s);
     if(topv == NULL || *topv != 2) { fprintf(stderr, "stack top expected 2 after pop\n"); return 2; }
 
-    // oben liegt nun 1
+    // pop -> now top should be 1
     s = pop(s);
     topv = (int *)top(s);
     if(topv == NULL || *topv != 1) { fprintf(stderr, "stack top expected 1 after pop\n"); return 3; }
 
-    // letzen Stapelinhalt holen
+    // pop last
     s = pop(s);
     if(s != NULL) { fprintf(stderr, "stack expected empty after popping all\n"); return 4; }
 
-    // Eigenen Speicher freigeben
+    // free stored data (stack does not free data)
-    free(a); 
+    free(a); free(b); free(c);
-    free(b); 
-    free(c);
 
-    // test clearStack mit leerem Stack
+    // test clearStack on empty and small stacks
     s = push(s, malloc(sizeof(int)));
     s = push(s, malloc(sizeof(int)));
     clearStack(s); // clearStack must free nodes but not payload; free payloads not necessary because we leaked intentionally for test of API
     // Note: above payloads are not freed (stack API spec); this test ensures clearStack doesn't crash.
-    // Funktioniert alles
+    // Success
     printf("test_stack: OK\n");
     return 0;
 }