Add logging framework.

DEBUG messages are completely optimized out if NDEBUG is defined.

include/ntcore_c.h

@@ -35,6 +35,19 @@ enum NT_EntryFlags {
   NT_PERSISTENT = 0x01
 };
 
+/** NetworkTables logging levels. */
+enum NT_LogLevel {
+  NT_LOG_CRITICAL = 50,
+  NT_LOG_ERROR = 40,
+  NT_LOG_WARNING = 30,
+  NT_LOG_INFO = 20,
+  NT_LOG_DEBUG = 10,
+  NT_LOG_DEBUG1 = 9,
+  NT_LOG_DEBUG2 = 8,
+  NT_LOG_DEBUG3 = 7,
+  NT_LOG_DEBUG4 = 6
+};
+
 /*
  * Structures
  */
@@ -309,6 +322,11 @@ void NT_DisposeConnectionInfoArray(struct NT_ConnectionInfo *arr, size_t count);
 /* timestamp */
 unsigned long long NT_Now(void);
 
+/* logging */
+typedef void (*NT_LogFunc)(unsigned int level, const char *file,
+                           unsigned int line, const char *msg);
+void NT_SetLogger(NT_LogFunc func, unsigned int min_level);
+
 #ifdef __cplusplus
 }
 #endif

include/ntcore_cpp.h

@@ -220,6 +220,11 @@ const char* LoadPersistent(
 /* timestamp */
 unsigned long long Now();
 
+/* logging */
+typedef std::function<void(unsigned int level, const char* file,
+                           unsigned int line, const char* msg)> LogFunc;
+void SetLogger(LogFunc func, unsigned int min_level);
+
 }  // namespace nt
 
 #endif  /* NTCORE_CPP_H_ */