为什么在 Qt cpp 源代码中为 .moc 文件添加一个包含很重要?
Why is it important to add an include for .moc file in a Qt cpp source code?
这是几个Qt示例中常用的步骤,包括这个:http://doc.qt.io/qt-5/qttestlib-tutorial1-example.html; 其中行 #include "testqstring.moc"
应该包含在文件的末尾.
This is a common step used in several Qt samples, including this one:
http://doc.qt.io/qt-5/qttestlib-tutorial1-example.html; where the line #include "testqstring.moc"
should be included in the end of the file.
我不明白为什么这是必要的.
I don't understand exactly why this is necessary.
如果您在 中使用
文件.这样做时:Q_OBJECT
宏定义 QObject
子类,则这是必要的.cpp
It's necessary if you define QObject
subclasses with the Q_OBJECT
macro in a .cpp
file. When you do so:
qmake
必须在您的 Makefile
中生成规则以在该 .cpp
上调用 moc
> 文件.
qmake
must generate rules inside your Makefile
to invoke moc
on that .cpp
file.
那个特殊的(hackish?)包含会触发 qmake
这样做,并告诉它哪个将是 moc
的输出文件 (teststring.moc
) 在您的 .cpp
上调用时.
That special (hackish?) inclusion triggers qmake
to do so, and tells it which would be moc
's output file (teststring.moc
) when invoked on your .cpp
.
为了编译moc
的输出(仍然是一堆C++代码),编译器必须看到你的类定义.否则,它会抱怨没有诸如 YourClass::staticMetaObject
之类的东西,因为它不知道 YourClass
存在.
In order to compile moc
's output (which is still a bunch of C++ code) the compiler must see your class definition. Otherwise, it will complain that there's no such thing as YourClass::staticMetaObject
and similar, because it has no idea that YourClass
exists.
通常在头文件中定义具有 Q_OBJECT
的类.moc
然后在其生成的输出中添加一个 #include "header.h"
,这意味着 moc
的输出可以被愉快地编译.
Typically one defines classes featuring Q_OBJECT
in a header file. moc
then adds a #include "header.h"
into its generated output, and this means moc
's output can be happily compiled.
但是如果您的类定义在 .cpp
中呢?您不能在 moc
的输出中 #include
一个 .cpp
文件,因为这会给您带来大量的重新定义错误.
But what if your class definition is inside a .cpp
? You can't #include
a .cpp
file in moc
's output, as that would give you tons of redefinition errors.
相反,您将#include
moc
的输出放在.cpp
中,以便将其编译在一起,每个人都很高兴.(这意味着 qmake
只会发出一个规则,说运行 moc
,而不是另一个规则告诉编译器编译 moc
的输出.)
Instead, you #include
moc
's output in your .cpp
, so that it gets compiled together and everyone is happy. (This means qmake
will only emit one rule saying to run moc
, but not another rule telling the compiler to compile moc
's output.)
从 2. 您还可以假设在 .h
中使用 Q_OBJECT
定义类不需要任何特殊包含.
From 2. you can also also desume that defining classes with Q_OBJECT
in a .h
does not require any special inclusion.
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