cmake父目录和子目录的变量传递

目录树

➜  test_pro6 tree -h 
.
├── [1.0K]  CMakeLists.txt
├── [4.0K]  app_hello
│   ├── [ 794]  CMakeLists.txt
│   ├── [ 280]  app_hello.c
│   └── [ 218]  app_hello.h
├── [ 276]  app_main.c
└── [4.0K]  build

子目录的cmake

set(TEST_CHILDREN_STR "children str" CACHE INTERNAL "Test Str") # 子cmake 和父cmake都可以访问
set(TEST_CHILDREN_PARENT_SCOPE_STR "children str" PARENT_SCOPE) # 只有父cmake可以访问

# 子cmake 和父cmake都可以访问
set(TEST_CHILDREN_ALL_SCOPE_STR "children str")
set(TEST_CHILDREN_ALL_SCOPE_STR ${TEST_CHILDREN_ALL_SCOPE_STR} PARENT_SCOPE)


message("TEST_PARENT_STR 2:" ${TEST_PARENT_STR})
message("TEST_CHILDREN_STR 2:" ${TEST_CHILDREN_STR})
message("TEST_CHILDREN_PARENT_SCOPE_STR 2:" ${TEST_CHILDREN_PARENT_SCOPE_STR})
message("TEST_CHILDREN_ALL_SCOPE_STR 2:" ${TEST_CHILDREN_ALL_SCOPE_STR})

父目录的cmake

message("TEST_PARENT_STR 1:" ${TEST_PARENT_STR})
message("TEST_CHILDREN_STR 1:" ${TEST_CHILDREN_STR})
message("TEST_CHILDREN_PARENT_SCOPE_STR 1:" ${TEST_CHILDREN_PARENT_SCOPE_STR})
message("TEST_CHILDREN_ALL_SCOPE_STR 1:" ${TEST_CHILDREN_ALL_SCOPE_STR})

add_subdirectory(${APP_HELLO_DIR})#请注意这个位置！！！

message("TEST_PARENT_STR 3:" ${TEST_PARENT_STR})
message("TEST_CHILDREN_STR 3:" ${TEST_CHILDREN_STR})
message("TEST_CHILDREN_PARENT_SCOPE_STR 3:" ${TEST_CHILDREN_PARENT_SCOPE_STR})
message("TEST_CHILDREN_ALL_SCOPE_STR 3:" ${TEST_CHILDREN_ALL_SCOPE_STR})

测试，首次执行cmake ..的结果如下
···

TEST_PARENT_STR 1:parent str
TEST_CHILDREN_STR 1:
TEST_CHILDREN_PARENT_SCOPE_STR 1:
TEST_CHILDREN_ALL_SCOPE_STR 1:

TEST_PARENT_STR 2:parent str
TEST_CHILDREN_STR 2:children str
TEST_CHILDREN_PARENT_SCOPE_STR 2:
TEST_CHILDREN_ALL_SCOPE_STR 2:children str

TEST_PARENT_STR 3:parent str
TEST_CHILDREN_STR 3:children str
TEST_CHILDREN_PARENT_SCOPE_STR 3:children str
TEST_CHILDREN_ALL_SCOPE_STR 3:children str

第二次执行 cmake ..的结果如下

TEST_PARENT_STR 1:parent str
TEST_CHILDREN_STR 1:children str #这一行不同，因为首次执行的时候，还未生成CMakeCache.txt
TEST_CHILDREN_PARENT_SCOPE_STR 1:
TEST_CHILDREN_ALL_SCOPE_STR 1:

TEST_PARENT_STR 2:parent str
TEST_CHILDREN_STR 2:children str
TEST_CHILDREN_PARENT_SCOPE_STR 2:
TEST_CHILDREN_ALL_SCOPE_STR 2:children str

TEST_PARENT_STR 3:parent str
TEST_CHILDREN_STR 3:children str
TEST_CHILDREN_PARENT_SCOPE_STR 3:children str
TEST_CHILDREN_ALL_SCOPE_STR 3:children str

通过以上测试，可以清晰的看到子目录和父目录的变量传递过程，
建议还是将add_subdirectory放在主cmake种较靠上的位置