格式:
if(expression) # then section. COMMAND1(ARGS ...) COMMAND2(ARGS ...) ... elseif(expression2) # elseif section. COMMAND1(ARGS ...) COMMAND2(ARGS ...) ... else() # else section. COMMAND1(ARGS ...) COMMAND2(ARGS ...) ... endif()
例子:
if(" ${CMAKE_SOURCE_DIR}" STREQUAL " ${CMAKE_BINARY_DIR}") message(FATAL_ERROR " FATAL: In-source builds are not allowed. You should create a separate directory for build files. ") endif()
STREQUAL 是 CMAKE 的关键字,用于字符串比较,相同返回 true
${CMAKE_SOURCE_DIR} 是 CMAKE 的自保留变量(拿来用就可以,含义已经确定),文件路径
${CMAKE_BINARY_DIR}是输出路径