Program Listing for File visibility_control_macros.h

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// Copyright 2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef RCUTILS__VISIBILITY_CONTROL_MACROS_H_
#define RCUTILS__VISIBILITY_CONTROL_MACROS_H_

// Defines macros to express whether a symbol is localed, imported, or exported
//
// Those macros are compatible with GCC, clang, and Microsoft Visual C++. They
// can be used to enforce which symbols of a library are publicly accessible.
//
// RCUTILS_IMPORT, RCUTILS_EXPORT, and RCUTILS_LOCAL are respectively declaring
// an imported, exported, or local symbol.
// RCUTILS_LOCAL can be used directly. However, RCUTILS_IMPORT, and
// RCUTILS_EXPORT may not be used directly. Every project need to provide
// an additional header called `visibility_macros.h` containing:
//
// #ifdef <project>_BUILDING_DLL
// # define <project>_PUBLIC RCUTILS_EXPORT
// #else
// # define <project>_PUBLIC RCUTILS_IMPORT
// #endif // !<project>_BUILDING_DLL
// #define <project>_LOCAL RCUTILS_LOCAL
//
// ...where "<project>" has been replaced by the project name, such as
// "MY_PROJECT".
// Your project CMakeLists.txt should also contain the following statement:
//
// target_compile_definitions(<your library> PRIVATE "<project>_BUILDING_DLL")
//
// A public (exported) class should then be tagged as <project>_PUBLIC, whereas
// a non-public class should be tagged with <project>_LOCAL.
//
// See GCC documentation: https://gcc.gnu.org/wiki/Visibility

#if defined(_MSC_VER) || defined(__CYGWIN__)
// Use the Windows syntax when compiling with Microsoft Visual C++.
//
// GCC on Windows also support this syntax. When compiling with cygwin,
// prefer using dllimport/dllexport are the semantic of those flags is closer
// to msvc++ behavior. See GCC documentation:
// https://gcc.gnu.org/onlinedocs/gcc/Microsoft-Windows-Function-Attributes.html
# define RCUTILS_IMPORT __declspec(dllimport)
# define RCUTILS_EXPORT __declspec(dllexport)
# define RCUTILS_LOCAL
#else  // defined(_MSC_VER) || defined(__CYGWIN__)
// On Linux, use the GCC syntax. This syntax is understood by other compilers
// such as clang, icpc, and xlc++.
# define RCUTILS_IMPORT __attribute__ ((visibility("default")))
# define RCUTILS_EXPORT __attribute__ ((visibility("default")))
# define RCUTILS_LOCAL  __attribute__ ((visibility("hidden")))
#endif  // !defined(_MSC_VER) && !defined(__CYGWIN__)

#endif  // RCUTILS__VISIBILITY_CONTROL_MACROS_H_