CMake：“SET(PODOFO_BUILD_SHARED而不是${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而不是${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行采用两个“布尔”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。
• 第二，如果只定义了PODOFO_BUILD_SHARED，那么第三行将反转PODOFO_BUILD_SHARED的值，不管它的初始值是什么。！
• 最后3行取PODOFO_BUILD_STATIC的倒置值，如果只定义PODOFO_BUILD_STATIC，则将其赋值给PODOFO_BUILD_STATIC。

然而，总体上看，这种行为似乎有点奇怪。我猜这(后三行)：

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：

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)

这样做更有意义:如果只定义了两个变量中的一个，则将另一个设置为相反的值。

"SET(PODOFO_BUILD_SHARED而不是${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

该变量可以通过几种方式预先在文件外部定义(例如从命令行定义，或者通过cmake-gui设置缓存变量)。