c++ - CMake: "SET(PODOFO_BUILD_SHARED NOT ${PODOFO_BUILD_SHARED})"是什么意思？

Question

# If the user hasn't told use specifically what they want, build only
# a static library.

IF(NOT DEFINED PODOFO_BUILD_SHARED AND NOT DEFINED PODOFO_BUILD_STATIC)
   SET(PODOFO_BUILD_STATIC TRUE)
   SET(PODOFO_BUILD_SHARED FALSE)
ENDIF(NOT DEFINED PODOFO_BUILD_SHARED AND NOT DEFINED PODOFO_BUILD_STATIC)

IF(DEFINED PODOFO_BUILD_SHARED AND NOT DEFINED PODOFO_BUILD_STATIC)
    SET(PODOFO_BUILD_SHARED NOT ${PODOFO_BUILD_SHARED})
ENDIF(DEFINED PODOFO_BUILD_SHARED AND NOT DEFINED PODOFO_BUILD_STATIC)

IF(NOT DEFINED PODOFO_BUILD_SHARED AND DEFINED PODOFO_BUILD_STATIC)
    SET(PODOFO_BUILD_SHARED NOT ${PODOFO_BUILD_STATIC})
ENDIF(NOT DEFINED PODOFO_BUILD_SHARED AND DEFINED PODOFO_BUILD_STATIC)

“SET(PODOFO_BUILD_SHARED NOT ${PODOFO_BUILD_SHARED})”是什么意思？在这些片段之前我看不到 PODOFO_BUILD_SHARED 变量的任何定义

Answer 1

• 前 4 行采用 2 个“ bool ”变量 PODOFO_BUILD_STATIC 和 PODOFO_BUILD_SHARED，如果它们都未定义，则将它们设置为默认值
• 如果只定义了 PODOFO_BUILD_SHARED，则后 3 行反转 PODOFO_BUILD_SHARED 的值，无论其初始值是什么。 奇怪!
• 如果只定义了 PODOFO_BUILD_STATIC，最后 3 行取 PODOFO_BUILD_STATIC 的反转值并将其分配给 PODOFO_BUILD_SHARED

但是，整体行为似乎有点奇怪。我的猜测是(第二三行):

IF(DEFINED PODOFO_BUILD_SHARED AND NOT DEFINED PODOFO_BUILD_STATIC)
    SET(PODOFO_BUILD_SHARED NOT ${PODOFO_BUILD_SHARED})
ENDIF(DEFINED PODOFO_BUILD_SHARED AND NOT DEFINED PODOFO_BUILD_STATIC)

应该是:

IF(DEFINED PODOFO_BUILD_SHARED AND NOT DEFINED PODOFO_BUILD_STATIC)
    SET(PODOFO_BUILD_STATIC NOT ${PODOFO_BUILD_SHARED})
ENDIF(DEFINED PODOFO_BUILD_SHARED AND NOT DEFINED PODOFO_BUILD_STATIC)

这样更有意义:如果只定义了 2 个变量中的一个，它将另一个设置为相反的值。

what does "SET(PODOFO_BUILD_SHARED NOT ${PODOFO_BUILD_SHARED})"means? before those snippet i cann't see any definition of PODOFO_BUILD_SHARED variable

可以通过多种方式预先在文件外部定义变量(例如，从命令行，或通过 cmake-gui 设置缓存变量)