如何打印使用 [=10=]() 设置的当前编译标志？

Question

我正在尝试打印为目标设置的编译标志。最好的方案是在配置和编译时间打印一行带有当前标志的行，但如果不可能，则仅在配置时间（或仅编译）（可接受的解决方案）。

这是我的测试 .c 文件：

#include <stdio.h>

int main() {
    printf("Hello, World!\n");
    return 0;
}

和CMakeLists.txt：

cmake_minimum_required(VERSION 3.10)
project(cmake_gcc_options_try_c C)

set(CMAKE_C_STANDARD 11)
set(CMAKE_C_STANDARD_REQUIRED ON)

add_executable(cmake_gcc_options_try_c main.c)

target_compile_options(cmake_gcc_options_try_c 
                       PUBLIC -W -Wall -Wextra -pedantic -pedantic-errors)

# This fails
message("-- Current compiler flags CMAKE_C_FLAGS are: ${CMAKE_C_FLAGS}")
message("-- Current compiler flags C_FLAGS are: ${C_FLAGS}")

和

cmake . && make

给出这个输出：

-- The C compiler identification is GNU 7.4.0
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Current compiler flags CMAKE_C_FLAGS are: 
-- Current compiler flags C_FLAGS are: 
-- Configuring done
-- Generating done
-- Build files have been written to: /home/user/Projects/cmake-gcc-options-try-c
Scanning dependencies of target cmake_gcc_options_try_c
[ 50%] Building C object CMakeFiles/cmake_gcc_options_try_c.dir/main.c.o
[100%] Linking C executable cmake_gcc_options_try_c
[100%] Built target cmake_gcc_options_try_c

为什么 CMAKE_C_FLAGS 和 C_FLAGS 打印时未定义？

如何在 make 命令上实现此打印：

[ 50%] Building C object CMakeFiles/cmake_gcc_options_try_c.dir/main.c.o
[ 50%] Current compiler flags are: -W -Wall -Wextra -pedantic -pedantic-errors -std=gnu11
[100%] Linking C executable cmake_gcc_options_try_c
[100%] Built target cmake_gcc_options_try_c

?

更新： Viktor Sergienko 提供了一个可行的解决方案，但有一个问题，它的打印效果不是很好：任何想法如何使它成为其他印刷品的格式？例如:

[ 50%] Building C object CMakeFiles/cmake_gcc_options_try_c.dir/main.c.o
[100%] Linking C executable cmake_gcc_options_try_c
[100%] Current compiler flags are: -W -Wall -Wextra -pedantic -pedantic-errors -std=gnu11
[100%] Built target cmake_gcc_options_try_c

第二个问题是 -std=gnu11 没有被打印出来（但是它被 set(CMAKE_C_STANDARD 11) 和 set(CMAKE_C_STANDARD_REQUIRED ON) 启用）

Answer 1

使用：

COMPILE_OPTIONS target property 获取 target-specific 编译标志；
add_custom_command 带有 POST_BUILD 选项来打印任何变量；

这为我提供了 ;-list 配置和编译时的选项：

cmake_minimum_required(VERSION 3.10)
project(cmake_gcc_options_try_c C)

set(CMAKE_C_STANDARD 11)
set(CMAKE_C_STANDARD_REQUIRED ON)

add_executable(cmake_gcc_options_try_c main.c)

target_compile_options(cmake_gcc_options_try_c 
                       PUBLIC -W -Wall -Wextra -pedantic -pedantic-errors)

get_target_property(MAIN_CFLAGS cmake_gcc_options_try_c COMPILE_OPTIONS)
# also see: COMPILE_DEFINITIONS INCLUDE_DIRECTORIES
message("-- Target compiler flags are: ${MAIN_CFLAGS}")

add_custom_command(TARGET cmake_gcc_options_try_c POST_BUILD
COMMAND echo built with the flags: ${MAIN_CFLAGS})

问题更新后更新：要获得C/CXX标准，查找C_STANDARD. If you wonder why CMake sets -gnu variant of the flag, it's because of CXX_EXTENSIONS默认为ON。

Update2：要将每个源文件的完整 compiler/linker 命令作为 JSON 文件，请设置 CMAKE_EXPORT_COMPILE_COMMANDS to ON (only works in CMake 3.5+, make and ninja generators). Credit for this piece goes to Florian's comment in this question.

如何打印使用 [=10=]() 设置的当前编译标志？

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如何打印使用 [​​=10=]() 设置的当前编译标志？

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如何打印使用 [=10=]() 设置的当前编译标志？