【提问】void description(QString &);要在．ｃｐｐ中定义吗？ [复制链接]

void description(QString &);要在．ｃｐｐ中定义吗？
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#include <qwidget.h>
#include <qevent.h>
#include <qstring.h>

class MouseSensor: public QWidget
{
  Q_OBJECT
public:
  MouseSensor(QWidget *parent=0,const char *name=0);
private:
  void emitDescription(const QString &,QMouseEvent *);
  virtual void mousePressEvent(QMouseEvent *event);
  virtual void mouseReleaseEvent(QMouseEvent *event);
  virtual void mouseDoubleClickEvent(QMouseEvent *event);
  virtual void mouseMoveEvent(QMouseEvent *event);
signals:
  void description(QString &);
};

#endif

/* mousesensor.cpp */
#include <qstring.h>
#include "mousesensor.h"

MouseSensor::MouseSensor(QWidget *parent)
  : QWidget(parent)
{
  setMinimumSize(300,300);
}
void MouseSensor::mousePressEvent(QMouseEvent *event)
{
  emitDescription(QString("Press: "),event);
}
void MouseSensor::mouseReleaseEvent(QMouseEvent *event)
{
  emitDescription(QString("Release: "),event);
}
void MouseSensor::mouseDoubleClickEvent(QMouseEvent *event)
{
  emitDescription(QString("DoubleClick: "),event);
}
void MouseSensor::mouseMoveEvent(QMouseEvent *event)
{
  emitDescription(QString("Move: "),event);
}
void MouseSensor::emitDescription(const QString &typeStr,
    QMouseEvent *event)
{
  QString btnStr(typeStr);
  ButtonState state = event->state();
  if(state & ControlButton)
    btnStr+= "Ctl-";
  if(state & AltButton)
    btnStr+= "Alt-";
  if(state & ShiftButton)
    btnStr+= "Shft-";
  if(state & LeftButton)
    btnStr += "(Lft)-";
  if(state & MidButton)
    btnStr += "(Mid)-";
  if(state & RightButton)
    btnStr += "(Rgt)-";
  ButtonState button = event->button();
  if(button & LeftButton)
    btnStr += "Lft";
  if(button & MidButton)
    btnStr += "Mid";
  if(button & RightButton)
    btnStr += "Rgt";

  QString str = QString("%1 (%2,%3)(%4,%5)")
    .arg(btnStr)
    .arg(event->x()).arg(event->y())
    .arg(event->globalX()).arg(event->globalY());

  emit description(str);
}

不需要。signal不需要

不需要，那能做什么， signal不是也可以看成函数吗，没有定义，功能不是不知道了吗

signal不是函数

在这里，什么作用？没有实现体，怎么知道做什么了!

信号是需要emit出去供slot接收的。