Fix VS linker warning regarding locally defined FLAGS_tryfromenv symbol.

src/gflags.cc

@@ -109,6 +109,11 @@
 #include "mutex.h"
 #include "util.h"
 
+// Export the following flags only if the gflags library is a DLL
+#ifndef GFLAGS_SHARED_LIBS
+#  undef  GFLAGS_DLL_DEFINE_FLAG
+#  define GFLAGS_DLL_DEFINE_FLAG
+#endif
 
 // Special flags, type 1: the 'recursive' flags.  They set another flag's val.
 DEFINE_string(flagfile,   "", "load flags from file");
@@ -395,8 +400,7 @@ const char* FlagValue::TypeName() const {
     assert(false);
     return "";
   }
-  // Directly indexing the strigns in the 'types' string, each of them
-  // is 7 bytes long.
+  // Directly indexing the strings in the 'types' string, each of them is 7 bytes long.
   return &types[type_ * 7];
 }
 

src/gflags_declare.h.in

@@ -72,18 +72,24 @@
 #  endif
 #endif
 
-// We always want to export defined variables, dll or no
-#if defined(_MSC_VER)
+// By default, we always want to export defined variables, assuming
+// that the DEFINE_FLAG macros are used within shared modules.
+#ifndef GFLAGS_DLL_DEFINE_FLAG
+#  if defined(_MSC_VER)
 #    define GFLAGS_DLL_DEFINE_FLAG __declspec(dllexport)
-#else
+#  else
 #    define GFLAGS_DLL_DEFINE_FLAG
+#  endif
 #endif
 
-// We always want to import declared variables, dll or no
-#if defined(_MSC_VER)
+// By default, we always want to export defined variables, assuming
+// that the DECLARE_FLAG macros are used within shared modules.
+#ifndef GFLAGS_DLL_DECLARE_FLAG
+#  if defined(_MSC_VER)
 #    define GFLAGS_DLL_DECLARE_FLAG __declspec(dllimport)
-#else
+#  else
 #    define GFLAGS_DLL_DECLARE_FLAG
+#  endif
 #endif
 
 // Export/import of STL class instantiations

test/gflags_unittest.cc

@@ -35,6 +35,11 @@
 #include "config_for_unittests.h"
 #include <gflags/gflags.h>
 
+#ifndef GFLAGS_SHARED_LIBS
+#  undef  GFLAGS_DLL_DECLARE_FLAG
+#  define GFLAGS_DLL_DECLARE_FLAG
+#endif
+
 #include <math.h>       // for isinf() and isnan()
 #include <stdio.h>
 #include <stdlib.h>