問題描述
為什么在 Qt cpp 源代碼中為 .moc 文件添加一個包含很重要?
Why is it important to add an include for .moc file in a Qt cpp source code?
這是幾個Qt示例中常用的步驟，包括這個:http://doc.qt.io/qt-5/qttestlib-tutorial1-example.html; 其中行 #include "testqstring.moc" 應(yīng)該包含在文件的末尾.
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.
我不明白為什么這是必要的.
I don't understand exactly why this is necessary.
推薦答案
如果您在 中使用 文件.這樣做時:Q_OBJECT 宏定義 QObject 子類，則這是必要的.cpp
It's necessary if you define QObject subclasses with the Q_OBJECT macro in a .cpp file. When you do so:
qmake必須在您的Makefile中生成規(guī)則以在該.cpp上調(diào)用moc> 文件.
qmakemust generate rules inside yourMakefileto invokemocon that.cppfile.
那個特殊的(hackish?)包含會觸發(fā) qmake 這樣做，并告訴它哪個將是 moc 的輸出文件 (teststring.moc) 在您的 .cpp 上調(diào)用時.
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.
為了編譯moc的輸出(仍然是一堆C++代碼)，編譯器必須看到你的類定義.否則，它會抱怨沒有諸如 YourClass::staticMetaObject 之類的東西，因為它不知道 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.
通常在頭文件中定義具有 Q_OBJECT 的類.moc 然后在其生成的輸出中添加一個 #include "header.h"，這意味著 moc 的輸出可以被愉快地編譯.
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.
但是如果您的類定義在 .cpp 中呢?您不能在 moc 的輸出中 #include 一個 .cpp 文件，因為這會給您帶來大量的重新定義錯誤.
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，您將#include moc 的輸出放在.cpp 中，以便將其編譯在一起，每個人都很高興.(這意味著 qmake 只會發(fā)出一個規(guī)則，說運行 moc，而不是另一個規(guī)則告訴編譯器編譯 moc 的輸出.)
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.)
從 2. 您還可以假設(shè)在 .h 中使用 Q_OBJECT 定義類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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