net: Add NET_API to net/base

base/compiler_specific.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_COMPILER_SPECIFIC_H_
 #define BASE_COMPILER_SPECIFIC_H_
 #pragma once
 
 #include "build/build_config.h"
 
@@ skipping 36 matching lines @@
 //
 // Example usage:
 // Foo::Foo() : x(NULL), ALLOW_THIS_IN_INITIALIZER_LIST(y(this)), z(3) {}
 //
 // Compiler warning C4355: 'this': used in base member initializer list:
 // http://msdn.microsoft.com/en-us/library/3c594ae3(VS.80).aspx
 #define ALLOW_THIS_IN_INITIALIZER_LIST(code) MSVC_PUSH_DISABLE_WARNING(4355) \
                                              code \
                                              MSVC_POP_WARNING()
 
+// Allows exporting a class that inherits from a non-exported base class.
+// This uses suppress instead of push/pop because the delimiter after the
+// declaration (either "," or "{") has to be placed before the pop macro.
+//
+// Example usage:
+// Class EXPORT_API Foo : NON_EXPORTED_BASE(public Bar) {

[brettw, 2011/05/18 06:06:18]

Did you mean "Class" to be lower-case?

[rvargas (doing something else), 2011/05/18 18:13:48]

Yes, fixed.

+//
+// MSVC Compiler warning C4275:
+// non dll-interface class 'Bar' used as base for dll-interface class 'Foo'
+// http://msdn.microsoft.com/en-us/library/3c594ae3(VS.80).aspx

[brettw, 2011/05/18 06:06:18]

Your URL doesn't seem to talk about C4275. I searched and found this page, is it
the right one?
http://msdn.microsoft.com/en-us/library/3tdb471s(VS.80).aspx

It might also be good to mention that you need to be very careful if you have
static data in the base class, and to see the article for more.

[rvargas (doing something else), 2011/05/18 18:13:48]

I added this to the comment:
// Note that this is intended to be used only when no access to the base class
// can be gained through the derived class. For more info, see
// http://msdn.microsoft.com/en-us/library/3tdb471s(VS.80).aspx

+#define NON_EXPORTED_BASE(code) MSVC_SUPPRESS_WARNING(4275) \
+                                code
+
 #else  // Not MSVC
 
 #define MSVC_SUPPRESS_WARNING(n)
 #define MSVC_PUSH_DISABLE_WARNING(n)
 #define MSVC_PUSH_WARNING_LEVEL(n)
 #define MSVC_POP_WARNING()
 #define MSVC_DISABLE_OPTIMIZE()
 #define MSVC_ENABLE_OPTIMIZE()
 #define ALLOW_THIS_IN_INITIALIZER_LIST(code) code
+#define NON_EXPORTED_BASE(code) code
 
 #endif  // COMPILER_MSVC
 
 
 // Annotate a variable indicating it's ok if the variable is not used.
 // (Typically used to silence a compiler warning when the assignment
 // is important for some other reason.)
 // Use like:
 //   int x ALLOW_UNUSED = ...;
 #if defined(COMPILER_GCC)
@@ skipping 38 matching lines @@
 #endif
 
 // WPRINTF_FORMAT is the same, but for wide format strings.
 // This doesn't appear to yet be implemented in any compiler.
 // See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38308 .
 #define WPRINTF_FORMAT(format_param, dots_param)
 // If available, it would look like:
 //   __attribute__((format(wprintf, format_param, dots_param)))
 
 #endif  // BASE_COMPILER_SPECIFIC_H_