CheckOBJCCompilerFlag

在 3.16 版被加入.

This module provides a command to check whether the Objective-C compiler supports a given flag.

在 CMake 專案中使用以下命令載入該模組：

include(CheckOBJCCompilerFlag)

命令

This module provides the following command:

check_objc_compiler_flag

Checks once whether the Objective-C compiler supports a given flag:

check_objc_compiler_flag(<flag> <variable>)

This command checks once that the <flag> is accepted by the OBJC compiler without producing a diagnostic message. Multiple flags can be specified in one argument as a string using a semicolon-separated list.

The result of the check is stored in the internal cache variable specified by <variable>, with boolean true for success and boolean false for failure.

A successful result only indicates that the compiler did not report an error when given the flag. Whether the flag has any effect, or the intended one, is outside the scope of this module.

備註

Since the underlying try_compile() command also uses flags from variables like CMAKE_<LANG>_FLAGS, unknown or unsupported flags in those variables may result in a false negative for this check.

影響檢查的變數

可以在呼叫此命令之前設定以下變數，以修改檢查的執行方式：

CMAKE_REQUIRED_FLAGS

一個以空格分隔的字串，包含要傳遞給編譯器的額外旗標。分號分隔列表將無法運作。CMAKE_<LANG>_FLAGS 及其關聯的特定組態 CMAKE_<LANG>_FLAGS_<CONFIG> 變數的內容會在該變數的內容之前自動預置到編譯器命令中。

CMAKE_REQUIRED_DEFINITIONS

一個編譯器定義的分號分隔列表，每個定義的形式為 -DFOO 或 -DFOO=bar。由檢查命令的結果變數引數所指定的名稱的定義也會自動新增。

CMAKE_REQUIRED_INCLUDES

一個要傳遞給編譯器的標頭搜尋路徑的分號分隔列表。這些將是唯一使用的標頭搜尋路徑；INCLUDE_DIRECTORIES 目錄屬性的內容將被忽略。

CMAKE_REQUIRED_LINK_OPTIONS

在 3.14 版被加入.

一個要新增到連結命令的選項的分號分隔列表（詳情請參見 try_compile()）。

CMAKE_REQUIRED_LIBRARIES

一個要新增到連結命令的程式庫的分號分隔列表。這些可以是系統程式庫的名稱，也可以是 Imported Targets`（詳情請參見 :command:`try_compile）。

CMAKE_REQUIRED_LINK_DIRECTORIES

在 3.31 版被加入.

一個要傳遞給連結器的程式庫搜尋路徑的分號分隔列表（詳情請參見 try_compile()）。

CMAKE_REQUIRED_QUIET

在 3.1 版被加入.

如果此變數的值為布林真值，則與檢查相關的所有狀態訊息都將被抑制。

CMAKE_TRY_COMPILE_TARGET_TYPE

Internally, the try_compile() command is used to perform the check, and this variable controls the type of target it creates. If this variable is set to EXECUTABLE (the default), the check compiles and links the test source code as an executable program. If set to STATIC_LIBRARY, the test source code is compiled but not linked.

範例

The following example demonstrates how to use this module to check the Objective-C compiler flag -fobjc-arc. The result of the check is stored in the internal cache variable HAVE_OBJC_ARC, and the flag is conditionally enabled using the target_compile_options() command. The $<COMPILE_LANGUAGE:...> generator expression ensures that the flag is added only to OBJC source files.

include(CheckOBJCCompilerFlag)
check_objc_compiler_flag(-fobjc-arc HAVE_OBJC_ARC)

if(HAVE_OBJC_ARC)
  target_compile_options(
    example
    PRIVATE $<$<COMPILE_LANGUAGE:OBJC>:-fobjc-arc>
  )
endif()

另請參見

  • The CheckCompilerFlag module for a more general command to check whether a compiler flag is supported.