Provide default stderr logger for INFO/WARN/ERR levels.

src/Log.cpp

@@ -7,10 +7,45 @@
 
 #include "Log.h"
 
+#include <cstdio>
+#ifdef _WIN32
+ #include <cstdlib>
+#else
+ #include <cstring>
+#endif
+
 using namespace nt;
 
 ATOMIC_STATIC_INIT(Logger)
 
-Logger::Logger() {}
+static void def_log_func(unsigned int level, const char* file,
+                         unsigned int line, const char* msg) {
+  if (level == 20) {
+    std::fprintf(stderr, "NT: %s\n", msg);
+    return;
+  }
+
+  const char* levelmsg;
+  if (level >= 50)
+    levelmsg = "CRITICAL";
+  else if (level >= 40)
+    levelmsg = "ERROR";
+  else if (level >= 30)
+    levelmsg = "WARNING";
+  else
+    return;
+#ifdef _WIN32
+  char fname[60];
+  char ext[10];
+  _splitpath_s(file, nullptr, 0, nullptr, 0, fname, 60, ext, 10);
+  std::fprintf(stderr, "NT: %s: %s (%s%s:%d)\n", levelmsg, msg, fname, ext,
+               line);
+#else
+  std::fprintf(stderr, "NT: %s: %s (%s:%d)\n", levelmsg, msg, basename(file),
+               line);
+#endif
+}
+
+Logger::Logger() : m_func(def_log_func) {}
 
 Logger::~Logger() {}

src/Log.h

@@ -45,7 +45,7 @@ class Logger {
   Logger();
 
   LogFunc m_func;
-  unsigned int m_min_level = 100;
+  unsigned int m_min_level = 20;
 
   ATOMIC_STATIC_DECL(Logger)
 };