"$< $< CONFIG:Debug>:Release>"是什么意思?在cmake中是什么意思? [英] What does "$<$<CONFIG:Debug>:Release>" mean in cmake?

问题描述

在 buildem_cmake_recipe.cmake 中，我看到了一个表达式:

In buildem_cmake_recipe.cmake, I saw an expression:

    externalproject_add_step(${_name} BuildOtherConfig
                        COMMAND ${CMAKE_COMMAND} --build ${BINARY_DIR} --config "$<$<CONFIG:Debug>:Release>$<$<CONFIG:Release>:Debug>" --target INSTALL
                        DEPENDEES install
                        )

$< $< CONFIG:Debug>:Release> $< $< CONFIG:Release>:Debug> 是什么意思?

推荐答案

这是CMake

That's a CMake generator expression. You can follow the link for a full discussion of what these are and what they can do. In short, it's a piece of text which CMake will evaluate at generate time (when it's done parsing all CMakeLists and is generating the buildsystem); it can evaluate to a different value for each configuration.

您那里的那个大概就是这个(伪代码):

The one you have there means roughly this (pseudo-code):

if current_configuration == "Debug"
  output "Release"
if current_configuration == "Release"
  output "Debug"

因此，如果当前配置为Debug，则整个表达式的计算结果将为 Release .如果当前配置为Release，它将评估为 Debug .注意，被添加的步骤被称为"BuildOtherConfig".因此，这种反向逻辑是有道理的.

So, if the current configuration is Debug, the whole expression will evaluate to Release. If the current configuration's Release, it will evaluate to Debug. Notice that the step being added is called "BuildOtherConfig," so this inverted logic makes sense.

其工作原理，再详细一点:

How it works, in a little more detail:

$<CONFIG:Debug>

如果当前配置为 Debug ，这将评估为 1 ，否则为 0 .

This will evaluate to a 1 if the current config is Debug, and to a 0 otherwise.

$<1:X>

计算为 X .

$<0:X>

计算为空字符串(无值).

Evaluates to an empty string (no value).

放在一起，我们有 $< $< CONFIG:Debug>:Release> .当前配置为 Debug 时，其评估结果如下:

Putting it together, we have $<$<CONFIG:Debug>:Release>. When the current config is Debug, it evaluates like this:

$<$<CONFIG:Debug>:Release>
$<1:Release>
Release

当当前配置不是 Debug 时，其评估结果如下:

When the current config is not Debug, it evaluates like this:

$<$<CONFIG:Debug>:Release>
$<0:Release>

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