Fix double ended queue did not print free strings

Because it is possible for to_string function to generate a new string
here and nothing else sees it after printing it is not guaranteed to be
freed leading to a memory leak. This does mean that if the string is
internal to a struct and expected to be used later then to_string should
duplicate said string (as noted in the documentation).

2 files changed, 9 insertions, 3 deletions

diff --git a/collections/double_ended_queue/double_ended_queue.adoc b/collections/double_ended_queue/double_ended_queue.adoc
index 52a085f..5daf03e 100644
--- a/collections/double_ended_queue/double_ended_queue.adoc
+++ b/collections/double_ended_queue/double_ended_queue.adoc
@@ -1,7 +1,7 @@
 Double Ended Queue
 ==================
 Tucker Evans
-v1.0.1, 2020-06-10
+v1.0.2, 2020-07-06
 
 A double ended queue implemented in a circular buffer.
 
@@ -514,6 +514,9 @@ Prints out the contents of the queue +self+ to +stdout+ (surounded by square bra
 function that takes a pointer to the type of elements stored in +self+ and
 returns a string representation.
 
+NOTE: Strings are freed after printing, therefore +strdup()+ should be used on
+any strings that are not for the sole purpose of printing here.
+
 Examples
 ^^^^^^^^
 [source,c]
@@ -524,7 +527,7 @@ Examples
 char* to_string(str)
 void *str;
 {
-	return str;
+	return strdup(str);
 }
 
 int main()
diff --git a/collections/double_ended_queue/double_ended_queue.c b/collections/double_ended_queue/double_ended_queue.c
index 28ed9dc..c08169d 100644
--- a/collections/double_ended_queue/double_ended_queue.c
+++ b/collections/double_ended_queue/double_ended_queue.c
@@ -147,12 +147,15 @@ deq *root;
 char* to_string(void*);
 {
 	int i, size;;
+	char *tmp;
 
 	size = deq_size(root);
 
 	printf("[");
 	for (i = 0; i < size; i++) {
-		printf("%s,", to_string(deq_index(root, i)));
+		printf("%s,", tmp = to_string(deq_index(root, i)));
+		free(tmp);
+		tmp = NULL;
 	}
 	printf("\b]\n");
 }