From ace33ff2c18c732e7ac30c49d95f7c35e06d7cee Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Fri, 4 Sep 2020 09:16:44 +0200
Subject: fix: Prüfe, ob 'data' wirklich dereferenziert werden kann
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---
 dlist.c  |  8 ++++++--
 queue.c  |  5 ++++-
 stack.c  | 14 +++++++-------
 stack2.c | 23 +++++++++++++----------
 4 files changed, 30 insertions(+), 20 deletions(-)

diff --git a/dlist.c b/dlist.c
index a2a5cfd..32258e8 100644
--- a/dlist.c
+++ b/dlist.c
@@ -112,7 +112,9 @@ dlist_pop_front(struct dlist *dlist, T *data)
 		else
 			element->next->prev = NULL;
 
-		*data = element->data;
+		if ( data != NULL ) {
+			*data = element->data;
+		}
 		free(element);
 
 		return true;
@@ -134,7 +136,9 @@ dlist_pop_back(struct dlist *dlist, T *data)
 		else
 			element->prev->next = NULL;
 
-		*data = element->data;
+		if ( data != NULL ) {
+			*data = element->data;
+		}
 		free(element);
 
 		return true;
diff --git a/queue.c b/queue.c
index e26acbb..2fb9c72 100644
--- a/queue.c
+++ b/queue.c
@@ -47,7 +47,10 @@ queue_get(struct queue *queue, T *data)
 {
 	if ( queue->head != NULL ) {
 		struct queue_item *next = queue->head->next;
-		*data                   = queue->head->data;
+
+		if ( data != NULL ) {
+			*data = queue->head->data;
+		}
 		free(queue->head);
 		queue->head = next;
 
diff --git a/stack.c b/stack.c
index fa89974..775269d 100644
--- a/stack.c
+++ b/stack.c
@@ -1,7 +1,7 @@
 /* Standard C */
+#include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <stdbool.h>
 
 /* Project */
 #include "util.h"
@@ -10,7 +10,7 @@ typedef int T;
 
 struct stack_item {
 	struct stack_item *next;
-	T data;
+	T                  data;
 };
 
 struct stack {
@@ -31,7 +31,7 @@ stack_push(struct stack *stack, T data)
 	if ( (new_item = malloc(sizeof(*new_item))) != NULL ) {
 		new_item->data = data;
 		new_item->next = stack->head;
-		stack->head = new_item;
+		stack->head    = new_item;
 	}
 	else
 		ERROR("out of memory");
@@ -42,7 +42,10 @@ stack_pop(struct stack *stack, T *data)
 {
 	if ( stack->head != NULL ) {
 		struct stack_item *next = stack->head->next;
-		*data = stack->head->data;
+
+		if ( data != NULL ) {
+			*data = stack->head->data;
+		}
 		free(stack->head);
 		stack->head = next;
 
@@ -93,6 +96,3 @@ main()
 
 	return EXIT_SUCCESS;
 }
-
-
-
diff --git a/stack2.c b/stack2.c
index 57dce4f..4c77ac2 100644
--- a/stack2.c
+++ b/stack2.c
@@ -1,13 +1,13 @@
+#include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <stdbool.h>
 
 #include "util.h"
 
 typedef int T;
 
 struct stack {
-	T *array;
+	T *    array;
 	size_t sz, p;
 };
 
@@ -15,8 +15,8 @@ void
 stack_init(struct stack *stack)
 {
 	stack->array = NULL;
-	stack->sz = 0;
-	stack->p = 0;
+	stack->sz    = 0;
+	stack->p     = 0;
 }
 
 bool
@@ -25,7 +25,7 @@ stack_push(struct stack *stack, T data)
 	if ( stack->array == NULL ) {
 		if ( (stack->array = malloc(10 * sizeof(*stack->array))) != NULL ) {
 			stack->sz = 10;
-			stack->p = 0;
+			stack->p  = 0;
 		}
 		else {
 			ERROR("out of memory");
@@ -35,11 +35,11 @@ stack_push(struct stack *stack, T data)
 
 	if ( stack->p == stack->sz ) {
 		size_t new_sz;
-		T *new_array;
+		T *    new_array;
 
-	   	if ( (new_array = realloc(stack->array, (new_sz = (stack->sz * 3 / 2)) * sizeof(*stack->array))) != NULL ) {
+		if ( (new_array = realloc(stack->array, (new_sz = (stack->sz * 3 / 2)) * sizeof(*stack->array))) != NULL ) {
 			stack->array = new_array;
-			stack->sz = new_sz;
+			stack->sz    = new_sz;
 		}
 		else {
 			ERROR("out of memory");
@@ -55,7 +55,11 @@ bool
 stack_pop(struct stack *stack, T *data)
 {
 	if ( stack->p != 0 ) {
-		*data = stack->array[--stack->p];
+		--stack->p;
+
+		if ( data != NULL ) {
+			*data = stack->array[stack->p];
+		}
 		return true;
 	}
 	else
@@ -97,4 +101,3 @@ main()
 
 	return EXIT_SUCCESS;
 }
-
-- 
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