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# 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

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1 回答 1

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  • 前 4 行采用 2 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
  • 如果仅定义了 PODOFO_BUILD_SHARED，则后 3 行反转 PODOFO_BUILD_SHARED 的值，无论其初始值是什么。奇怪的！
  • 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。我的猜测是这个（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)

应该：

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)

通过这种方式，它更有意义：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。

“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

变量可以在文件外部以多种方式预先定义（例如，从命令行，或通过设置缓存变量cmake-gui）

于 2013-11-07T12:11:08.543 回答