fix: Pass std::string directly, no need for c_str() call
diff --git a/test/gflags_unittest.cc b/test/gflags_unittest.cc
index cc3049b..f205466 100644
--- a/test/gflags_unittest.cc
+++ b/test/gflags_unittest.cc
@@ -1514,7 +1514,7 @@
   // The non-recommended way:
   FLAGS_changed_bool2 = true;
 
-  SetUsageMessage(usage_message.c_str());
+  SetUsageMessage(usage_message);
   SetVersionString("test_version");
   ParseCommandLineFlags(&argc, &argv, true);
   MakeTmpdir(&FLAGS_test_tmpdir);