Return allocated string instead of pointer to a string literal

Issue #110

Signed-off-by: Szczepan Zalega <szczepan@nitrokey.com>

2 files changed, 5 insertions, 3 deletions

diff --git a/NK_C_API.cc b/NK_C_API.cc
index b245940..c398e95 100644
--- a/NK_C_API.cc
+++ b/NK_C_API.cc
@@ -85,7 +85,7 @@ const char* get_with_string_result(T func){
     catch (const DeviceCommunicationException &deviceException){
       NK_last_command_status = 256-deviceException.getType();
     }
-    return "";
+    return strndup("", MAXIMUM_STR_REPLY_LENGTH);
 }
 
 template <typename T>
@@ -640,7 +640,7 @@ extern "C" {
 				res += a+";";
 			}
 			if (res.size()>0) res.pop_back(); // remove last delimiter char
-			return strndup(res.c_str(), 8192); //this buffer size sets limit to over 200 devices ID's
+			return strndup(res.c_str(), MAXIMUM_STR_REPLY_LENGTH);
 		});
 	}
 
diff --git a/NK_C_API.h b/NK_C_API.h
index 3a6aa2a..858f046 100644
--- a/NK_C_API.h
+++ b/NK_C_API.h
@@ -28,13 +28,15 @@
 #ifdef _MSC_VER
 #define NK_C_API __declspec(dllexport)
 #else
-#define NK_C_API 
+#define NK_C_API
 #endif
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+  static const int MAXIMUM_STR_REPLY_LENGTH = 8192;
+
         /**
          * The Nitrokey device models supported by the API.
          */