AC_SYS_LARGEFILE 使用 CMake
AC_SYS_LARGEFILE with CMake
我声明我从未使用过 autoconf 工具。
现在我正在将一个小项目从 autoconf 迁移到 cmake，并且我 运行 迁移到 AC_SYS_LARGEFILE。我对 AC_SYS_LARGEFILE 了解不多，只是它是一种检查，以了解例如 off_t 是 4 字节还是 8 字节。
出于好奇，我想了解哪些是AC_SYS_LARGEFILE的典型用例。
来到真正的问题，我还需要 AC_SYS_LARGEFILE 用于 CMake 吗？
如果是，CMake 中是否已经存在一种机制，还是我应该自己实现？
你几乎是正确的。 AC_SYS_LARGEFILE autoconf 宏 为程序启用 大文件支持（8 字节文件偏移量）。对于某些编译器，还必须定义其他编译器定义才能处理大文件。
据我所知，目前还没有对 CMake 本机的任何支持。但是，有一些 CMake 项目已经创建了自己的解决方案；在 WireShark and the OpenJPEG repositories. The code in each of these appears to be adapted from the Gromacs Project.
中查看这些文件
为了完整起见，这里是 WireShark CMake 文件，展示了如何测试程序中是否需要大文件支持：
# This code was copied from http://www.gromacs.org/
# and its toplevel COPYING file starts with:
#
# GROMACS is free software, distributed under the GNU General Public License
# (GPL) Version 2.
# - Define macro to check large file support
#
# GMX_TEST_LARGE_FILES(VARIABLE)
#
# VARIABLE will be set to true if 64-bit file support is available.
# This macro will also set defines as necessary to enable large file
# support, for instance:
# _LARGE_FILES
# _LARGEFILE_SOURCE
# _FILE_OFFSET_BITS=64
#
# However, it is YOUR job to make sure these defines are set in a cmakedefine so they
# end up in a config.h file that is included in your source if necessary!
MACRO(GMX_TEST_LARGE_FILES VARIABLE)
IF(NOT DEFINED ${VARIABLE})
if(CMAKE_C_COMPILER_ID MATCHES "MSVC")
#
# This is Visual Studio; Visual Studio has supported
# _fseeki64 and _ftelli64 since Visual Studio 2005 / MSVCR80,
# and we require newer versions, so we know we have them.
#
MESSAGE(STATUS "_fseeki64 and _ftelli64 are present")
else(CMAKE_C_COMPILER_ID MATCHES "MSVC")
#
# This is UN*X, or some other Windows compiler.
#
# For UN*X, we do the Large File Support tests, to see
# whether it's present and, if so what we need to define
# to enable it.
#
# XXX - what's the right thing to do on Windows with,
# for example, MinGW?
#
# On most platforms it is probably overkill to first test
# the flags for 64-bit off_t, and then separately fseeko.
# However, in the future we might have 128-bit seek offsets
# to support 128-bit filesystems that allow 128-bit offsets
# (ZFS), so it might be dangerous to indiscriminately set
# e.g. _FILE_OFFSET_BITS=64.
#
MESSAGE(STATUS "Checking for 64-bit off_t")
# First check without any special flags
TRY_COMPILE(FILE64_OK "${CMAKE_BINARY_DIR}"
"${CMAKE_SOURCE_DIR}/cmake/TestFileOffsetBits.c")
if(FILE64_OK)
MESSAGE(STATUS "64-bit off_t is present with no special flags")
endif(FILE64_OK)
if(NOT FILE64_OK)
# Test with _FILE_OFFSET_BITS=64
TRY_COMPILE(FILE64_OK "${CMAKE_BINARY_DIR}"
"${CMAKE_SOURCE_DIR}/cmake/TestFileOffsetBits.c"
COMPILE_DEFINITIONS "-D_FILE_OFFSET_BITS=64" )
if(FILE64_OK)
MESSAGE(STATUS "64-bit off_t is present with _FILE_OFFSET_BITS=64")
set(_FILE_OFFSET_BITS 64 CACHE INTERNAL "64-bit off_t requires _FILE_OFFSET_BITS=64")
endif(FILE64_OK)
endif(NOT FILE64_OK)
if(NOT FILE64_OK)
# Test with _LARGE_FILES
TRY_COMPILE(FILE64_OK "${CMAKE_BINARY_DIR}"
"${CMAKE_SOURCE_DIR}/cmake/TestFileOffsetBits.c"
COMPILE_DEFINITIONS "-D_LARGE_FILES" )
if(FILE64_OK)
MESSAGE(STATUS "64-bit off_t is present with _LARGE_FILES")
set(_LARGE_FILES 1 CACHE INTERNAL "64-bit off_t requires _LARGE_FILES")
endif(FILE64_OK)
endif(NOT FILE64_OK)
if(NOT FILE64_OK)
# Test with _LARGEFILE_SOURCE
TRY_COMPILE(FILE64_OK "${CMAKE_BINARY_DIR}"
"${CMAKE_SOURCE_DIR}/cmake/TestFileOffsetBits.c"
COMPILE_DEFINITIONS "-D_LARGEFILE_SOURCE" )
if(FILE64_OK)
MESSAGE(STATUS "64-bit off_t is present with _LARGEFILE_SOURCE")
set(_LARGEFILE_SOURCE 1 CACHE INTERNAL "64-bit off_t requires _LARGEFILE_SOURCE")
endif(FILE64_OK)
endif(NOT FILE64_OK)
if(NOT FILE64_OK)
MESSAGE(STATUS "64-bit file offset support not available")
else(NOT FILE64_OK)
# Set the flags we might have determined to be required above
configure_file("${CMAKE_SOURCE_DIR}/cmake/TestLargeFiles.c.cmakein"
"${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/TestLargeFiles.c")
#
# If this is Windows, assume we have _fseeki64/_ftelli64
# available. If this is UN*X, check for fseeko/ftello.
#
if(NOT WIN32)
MESSAGE(STATUS "Checking for fseeko/ftello")
# Test if ftello/fseeko are available
TRY_COMPILE(FSEEKO_COMPILE_OK "${CMAKE_BINARY_DIR}"
"${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/TestLargeFiles.c")
if(FSEEKO_COMPILE_OK)
MESSAGE(STATUS "Checking for fseeko/ftello - present")
endif(FSEEKO_COMPILE_OK)
if(NOT FSEEKO_COMPILE_OK)
# glibc 2.2 neds _LARGEFILE_SOURCE for fseeko (but not 64-bit off_t...)
TRY_COMPILE(FSEEKO_COMPILE_OK "${CMAKE_BINARY_DIR}"
"${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/TestLargeFiles.c"
COMPILE_DEFINITIONS "-D_LARGEFILE_SOURCE" )
if(FSEEKO_COMPILE_OK)
MESSAGE(STATUS "Checking for fseeko/ftello - present with _LARGEFILE_SOURCE")
set(_LARGEFILE_SOURCE 1 CACHE INTERNAL "64-bit fseeko requires _LARGEFILE_SOURCE")
endif(FSEEKO_COMPILE_OK)
endif(NOT FSEEKO_COMPILE_OK)
if(FSEEKO_COMPILE_OK)
SET(${VARIABLE} 1 CACHE INTERNAL "Result of test for large file support" FORCE)
set(HAVE_FSEEKO 1 CACHE INTERNAL "64-bit fseeko is available" FORCE)
else(FSEEKO_COMPILE_OK)
MESSAGE(STATUS "Checking for fseeko/ftello - not found")
SET(${VARIABLE} 0 CACHE INTERNAL "Result of test for large file support" FORCE)
endif(FSEEKO_COMPILE_OK)
endif(NOT WIN32)
endif(NOT FILE64_OK)
endif(CMAKE_C_COMPILER_ID MATCHES "MSVC")
ENDIF(NOT DEFINED ${VARIABLE})
ENDMACRO(GMX_TEST_LARGE_FILES VARIABLE)
我声明我从未使用过 autoconf 工具。
现在我正在将一个小项目从 autoconf 迁移到 cmake，并且我 运行 迁移到 AC_SYS_LARGEFILE。我对 AC_SYS_LARGEFILE 了解不多，只是它是一种检查，以了解例如 off_t 是 4 字节还是 8 字节。
出于好奇，我想了解哪些是AC_SYS_LARGEFILE的典型用例。
来到真正的问题，我还需要 AC_SYS_LARGEFILE 用于 CMake 吗？
如果是，CMake 中是否已经存在一种机制，还是我应该自己实现？
你几乎是正确的。 AC_SYS_LARGEFILE autoconf 宏 为程序启用 大文件支持（8 字节文件偏移量）。对于某些编译器，还必须定义其他编译器定义才能处理大文件。
据我所知，目前还没有对 CMake 本机的任何支持。但是，有一些 CMake 项目已经创建了自己的解决方案；在 WireShark and the OpenJPEG repositories. The code in each of these appears to be adapted from the Gromacs Project.
中查看这些文件为了完整起见，这里是 WireShark CMake 文件，展示了如何测试程序中是否需要大文件支持：
# This code was copied from http://www.gromacs.org/
# and its toplevel COPYING file starts with:
#
# GROMACS is free software, distributed under the GNU General Public License
# (GPL) Version 2.
# - Define macro to check large file support
#
# GMX_TEST_LARGE_FILES(VARIABLE)
#
# VARIABLE will be set to true if 64-bit file support is available.
# This macro will also set defines as necessary to enable large file
# support, for instance:
# _LARGE_FILES
# _LARGEFILE_SOURCE
# _FILE_OFFSET_BITS=64
#
# However, it is YOUR job to make sure these defines are set in a cmakedefine so they
# end up in a config.h file that is included in your source if necessary!
MACRO(GMX_TEST_LARGE_FILES VARIABLE)
IF(NOT DEFINED ${VARIABLE})
if(CMAKE_C_COMPILER_ID MATCHES "MSVC")
#
# This is Visual Studio; Visual Studio has supported
# _fseeki64 and _ftelli64 since Visual Studio 2005 / MSVCR80,
# and we require newer versions, so we know we have them.
#
MESSAGE(STATUS "_fseeki64 and _ftelli64 are present")
else(CMAKE_C_COMPILER_ID MATCHES "MSVC")
#
# This is UN*X, or some other Windows compiler.
#
# For UN*X, we do the Large File Support tests, to see
# whether it's present and, if so what we need to define
# to enable it.
#
# XXX - what's the right thing to do on Windows with,
# for example, MinGW?
#
# On most platforms it is probably overkill to first test
# the flags for 64-bit off_t, and then separately fseeko.
# However, in the future we might have 128-bit seek offsets
# to support 128-bit filesystems that allow 128-bit offsets
# (ZFS), so it might be dangerous to indiscriminately set
# e.g. _FILE_OFFSET_BITS=64.
#
MESSAGE(STATUS "Checking for 64-bit off_t")
# First check without any special flags
TRY_COMPILE(FILE64_OK "${CMAKE_BINARY_DIR}"
"${CMAKE_SOURCE_DIR}/cmake/TestFileOffsetBits.c")
if(FILE64_OK)
MESSAGE(STATUS "64-bit off_t is present with no special flags")
endif(FILE64_OK)
if(NOT FILE64_OK)
# Test with _FILE_OFFSET_BITS=64
TRY_COMPILE(FILE64_OK "${CMAKE_BINARY_DIR}"
"${CMAKE_SOURCE_DIR}/cmake/TestFileOffsetBits.c"
COMPILE_DEFINITIONS "-D_FILE_OFFSET_BITS=64" )
if(FILE64_OK)
MESSAGE(STATUS "64-bit off_t is present with _FILE_OFFSET_BITS=64")
set(_FILE_OFFSET_BITS 64 CACHE INTERNAL "64-bit off_t requires _FILE_OFFSET_BITS=64")
endif(FILE64_OK)
endif(NOT FILE64_OK)
if(NOT FILE64_OK)
# Test with _LARGE_FILES
TRY_COMPILE(FILE64_OK "${CMAKE_BINARY_DIR}"
"${CMAKE_SOURCE_DIR}/cmake/TestFileOffsetBits.c"
COMPILE_DEFINITIONS "-D_LARGE_FILES" )
if(FILE64_OK)
MESSAGE(STATUS "64-bit off_t is present with _LARGE_FILES")
set(_LARGE_FILES 1 CACHE INTERNAL "64-bit off_t requires _LARGE_FILES")
endif(FILE64_OK)
endif(NOT FILE64_OK)
if(NOT FILE64_OK)
# Test with _LARGEFILE_SOURCE
TRY_COMPILE(FILE64_OK "${CMAKE_BINARY_DIR}"
"${CMAKE_SOURCE_DIR}/cmake/TestFileOffsetBits.c"
COMPILE_DEFINITIONS "-D_LARGEFILE_SOURCE" )
if(FILE64_OK)
MESSAGE(STATUS "64-bit off_t is present with _LARGEFILE_SOURCE")
set(_LARGEFILE_SOURCE 1 CACHE INTERNAL "64-bit off_t requires _LARGEFILE_SOURCE")
endif(FILE64_OK)
endif(NOT FILE64_OK)
if(NOT FILE64_OK)
MESSAGE(STATUS "64-bit file offset support not available")
else(NOT FILE64_OK)
# Set the flags we might have determined to be required above
configure_file("${CMAKE_SOURCE_DIR}/cmake/TestLargeFiles.c.cmakein"
"${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/TestLargeFiles.c")
#
# If this is Windows, assume we have _fseeki64/_ftelli64
# available. If this is UN*X, check for fseeko/ftello.
#
if(NOT WIN32)
MESSAGE(STATUS "Checking for fseeko/ftello")
# Test if ftello/fseeko are available
TRY_COMPILE(FSEEKO_COMPILE_OK "${CMAKE_BINARY_DIR}"
"${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/TestLargeFiles.c")
if(FSEEKO_COMPILE_OK)
MESSAGE(STATUS "Checking for fseeko/ftello - present")
endif(FSEEKO_COMPILE_OK)
if(NOT FSEEKO_COMPILE_OK)
# glibc 2.2 neds _LARGEFILE_SOURCE for fseeko (but not 64-bit off_t...)
TRY_COMPILE(FSEEKO_COMPILE_OK "${CMAKE_BINARY_DIR}"
"${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/TestLargeFiles.c"
COMPILE_DEFINITIONS "-D_LARGEFILE_SOURCE" )
if(FSEEKO_COMPILE_OK)
MESSAGE(STATUS "Checking for fseeko/ftello - present with _LARGEFILE_SOURCE")
set(_LARGEFILE_SOURCE 1 CACHE INTERNAL "64-bit fseeko requires _LARGEFILE_SOURCE")
endif(FSEEKO_COMPILE_OK)
endif(NOT FSEEKO_COMPILE_OK)
if(FSEEKO_COMPILE_OK)
SET(${VARIABLE} 1 CACHE INTERNAL "Result of test for large file support" FORCE)
set(HAVE_FSEEKO 1 CACHE INTERNAL "64-bit fseeko is available" FORCE)
else(FSEEKO_COMPILE_OK)
MESSAGE(STATUS "Checking for fseeko/ftello - not found")
SET(${VARIABLE} 0 CACHE INTERNAL "Result of test for large file support" FORCE)
endif(FSEEKO_COMPILE_OK)
endif(NOT WIN32)
endif(NOT FILE64_OK)
endif(CMAKE_C_COMPILER_ID MATCHES "MSVC")
ENDIF(NOT DEFINED ${VARIABLE})
ENDMACRO(GMX_TEST_LARGE_FILES VARIABLE)