GenerateExportHeader

Function for generation of export macros for libraries

This module provides the function GENERATE_EXPORT_HEADER().

Added in version 3.12: Added support for C projects. Previous versions supported C++ project only.

The GENERATE_EXPORT_HEADER function can be used to generate a file suitable for preprocessor inclusion which contains EXPORT macros to be used in library classes:

GENERATE_EXPORT_HEADER( LIBRARY_TARGET
          [BASE_NAME <base_name>]
          [EXPORT_MACRO_NAME <export_macro_name>]
          [EXPORT_FILE_NAME <export_file_name>]
          [DEPRECATED_MACRO_NAME <deprecated_macro_name>]
          [NO_EXPORT_MACRO_NAME <no_export_macro_name>]
          [INCLUDE_GUARD_NAME <include_guard_name>]
          [STATIC_DEFINE <static_define>]
          [NO_DEPRECATED_MACRO_NAME <no_deprecated_macro_name>]
          [DEFINE_NO_DEPRECATED]
          [PREFIX_NAME <prefix_name>]
          [CUSTOM_CONTENT_FROM_VARIABLE <variable>]
)

The target properties CXX_VISIBILITY_PRESET and VISIBILITY_INLINES_HIDDEN can be used to add the appropriate compile flags for targets. See the documentation of those target properties, and the convenience variables CMAKE_CXX_VISIBILITY_PRESET and CMAKE_VISIBILITY_INLINES_HIDDEN.

By default GENERATE_EXPORT_HEADER() generates macro names in a file name determined by the name of the library. This means that in the simplest case, users of GenerateExportHeader will be equivalent to:

set(CMAKE_CXX_VISIBILITY_PRESET hidden)
set(CMAKE_VISIBILITY_INLINES_HIDDEN 1)
add_library(somelib someclass.cpp)
generate_export_header(somelib)
install(TARGETS somelib DESTINATION ${LIBRARY_INSTALL_DIR})
install(FILES
 someclass.h
 ${PROJECT_BINARY_DIR}/somelib_export.h DESTINATION ${INCLUDE_INSTALL_DIR}
)

And in the ABI header files:

#include "somelib_export.h"
class SOMELIB_EXPORT SomeClass {
  ...
};

The CMake fragment will generate a file in the ${CMAKE_CURRENT_BINARY_DIR} called somelib_export.h containing the macros SOMELIB_EXPORT, SOMELIB_NO_EXPORT, SOMELIB_DEPRECATED, SOMELIB_DEPRECATED_EXPORT and SOMELIB_DEPRECATED_NO_EXPORT. They will be followed by content taken from the variable specified by the CUSTOM_CONTENT_FROM_VARIABLE option, if any. The resulting file should be installed with other headers in the library.

The BASE_NAME argument can be used to override the file name and the names used for the macros:

add_library(somelib someclass.cpp)
generate_export_header(somelib
  BASE_NAME other_name
)

Generates a file called other_name_export.h containing the macros OTHER_NAME_EXPORT, OTHER_NAME_NO_EXPORT and OTHER_NAME_DEPRECATED etc.

The BASE_NAME may be overridden by specifying other options in the function. For example:

add_library(somelib someclass.cpp)
generate_export_header(somelib
  EXPORT_MACRO_NAME OTHER_NAME_EXPORT
)

creates the macro OTHER_NAME_EXPORT instead of SOMELIB_EXPORT, but other macros and the generated file name is as default:

add_library(somelib someclass.cpp)
generate_export_header(somelib
  DEPRECATED_MACRO_NAME KDE_DEPRECATED
)

creates the macro KDE_DEPRECATED instead of SOMELIB_DEPRECATED.

If LIBRARY_TARGET is a static library, macros are defined without values.

If the same sources are used to create both a shared and a static library, the uppercased symbol ${BASE_NAME}_STATIC_DEFINE should be used when building the static library:

add_library(shared_variant SHARED ${lib_SRCS})
add_library(static_variant ${lib_SRCS})
generate_export_header(shared_variant BASE_NAME libshared_and_static)
set_target_properties(static_variant PROPERTIES
  COMPILE_FLAGS -DLIBSHARED_AND_STATIC_STATIC_DEFINE)

This will cause the export macros to expand to nothing when building the static library.

If DEFINE_NO_DEPRECATED is specified, then a macro ${BASE_NAME}_NO_DEPRECATED will be defined This macro can be used to remove deprecated code from preprocessor output:

option(EXCLUDE_DEPRECATED "Exclude deprecated parts of the library" FALSE)
if (EXCLUDE_DEPRECATED)
  set(NO_BUILD_DEPRECATED DEFINE_NO_DEPRECATED)
endif()
generate_export_header(somelib ${NO_BUILD_DEPRECATED})

And then in somelib:

class SOMELIB_EXPORT SomeClass
{
public:
#ifndef SOMELIB_NO_DEPRECATED
  SOMELIB_DEPRECATED void oldMethod();
#endif
};

#ifndef SOMELIB_NO_DEPRECATED
void SomeClass::oldMethod() {  }
#endif

If PREFIX_NAME is specified, the argument will be used as a prefix to all generated macros.

For example:

generate_export_header(somelib PREFIX_NAME VTK_)

Generates the macros VTK_SOMELIB_EXPORT etc.

Added in version 3.1: Library target can be an OBJECT library.

Added in version 3.7: Added the CUSTOM_CONTENT_FROM_VARIABLE option.

Added in version 3.11: Added the INCLUDE_GUARD_NAME option.

ADD_COMPILER_EXPORT_FLAGS( [<output_variable>] )

Deprecated since version 3.0: Set the target properties CXX_VISIBILITY_PRESET and VISIBILITY_INLINES_HIDDEN instead.

The ADD_COMPILER_EXPORT_FLAGS function adds -fvisibility=hidden to CMAKE_CXX_FLAGS if supported, and is a no-op on Windows which does not need extra compiler flags for exporting support. You may optionally pass a single argument to ADD_COMPILER_EXPORT_FLAGS that will be populated with the CXX_FLAGS required to enable visibility support for the compiler/architecture in use.