在 Qt 5 中，QObject::connect()有五個重載：

QMetaObject::Connection connect(const QObject *, const char *,
                                const QObject *, const char *,
                                Qt::ConnectionType);
 
QMetaObject::Connection connect(const QObject *, const QMetaMethod &,
                                const QObject *, const QMetaMethod &,
                                Qt::ConnectionType);
 
QMetaObject::Connection connect(const QObject *, const char *,
                                const char *,
                                Qt::ConnectionType) const;
 
QMetaObject::Connection connect(const QObject *, PointerToMemberFunction,
                                const QObject *, PointerToMemberFunction,
                                Qt::ConnectionType)
 
QMetaObject::Connection connect(const QObject *, PointerToMemberFunction,
                                Functor);

最常用的一般形式：

1 connect(sender,   signal,   receiver,   slot);

sender：發出信號的對象，類型為QObject*

signal：發出的信號，類型為const char*

receiver：接收信號的對象，類型為QObject*

slot：接收信號後調用的函數（槽函數），類型為const char*

註意：槽函數的參數類型要和信號的一致，參數數量小於等於信號數量。

自定義槽函數：

 1 #include <QObject>
 2  
 3 ////////// newspaper.h
 4 class Newspaper : public
 
 QObject
 5 {
 6     Q_OBJECT
 7 public:
 8     Newspaper(const QString & name) :
 9         m_name(name)
10     {
11     }
12  
13     void send()
14     {
15         emit newPaper(m_name);
16     }
17  
18 signals:
19     void newPaper(const QString &name);
20  
21 private:
22     QString m_name;
 
23 };
24  
25 ////////// reader.h
26 #include <QObject>
27 #include <QDebug>
28  
29 class Reader : public QObject
30 {
31     Q_OBJECT
32 public:
33     Reader() {}
34  
35     void receiveNewspaper(const QString & name)
36     {
37         qDebug() << "Receives Newspaper: " << name;
38     }
39 };
40  
41 ////////// main.cpp
42 #include <QCoreApplication>
43  
44 #include "newspaper.h"
45 #include "reader.h"
46  
47 int main(int argc, char *argv[])
48 {
49     QCoreApplication app(argc, argv);
50  
51     Newspaper newspaper("Newspaper A");
52     Reader reader;
53     QObject::connect(&newspaper, &Newspaper::newPaper,
54                      &reader,    &Reader::receiveNewspaper);
55     newspaper.send();
56  
57     return app.exec();
58 }

要使用槽函數功能，自定義的類必須要繼承QObject類，並在第一行代碼上寫上Q_OBJECT（無論是否使用信號槽，凡是QObject的子類都應該寫上）。

Newspaper類有個signals代碼塊，它裏面的就是該類的信號。信號是一個個函數名，返回值是void，不需要添加任何實現。

send()函數，只有一個語句emit newPaper(m_name); 。emit意思是發出信號，此處為發出newPaper信號，參數為m_name。

在main函數中，使用QObject::connect()來連接信號和槽。

原文：

https://www.devbean.net/2012/08/qt-study-road-2-signal-slot/

https://www.devbean.net/2012/08/qt-study-road-2-custom-signal-slot/

Qt5學習筆記 | 信號槽