switch的子项必须为整数，if没有这个限制。
如此说来，if、else if岂非包括switch的所有应用场景了？可以完全取代switch。
之所以很多人用switch，是不是因为它的写法，看起来代码很工整好看？
- C/C++ code
void calculatePaintRect(){ if ((!m_bMousePressed) || (NO_ACTION==enAction)) { return; } //上一次鼠标位置与这次鼠标位置的差额 QPoint ptEvent = event->pos(); int xDiff = ptEvent.x() - m_ptLast.x(); int yDiff = ptEvent.y() - m_ptLast.y(); QRect rectAdjust = m_rectOfRedLine; //或者移动，或者缩放 if (DRAG_TOP_LEFT == enAction) { //缩放（右下不变） xDiff = ptEvent.x() - m_rectOfRedLine.x(); yDiff = ptEvent.y() - m_rectOfRedLine.y(); rectAdjust.adjust(xDiff, yDiff, 0, 0); if (SCALE_FIX == m_eumScaleType) { int newWidth = rectAdjust.width(); int newHeight = newWidth * CAPTURE_HEIGHT / CAPTURE_WIDTH; rectAdjust.setLeft(rectAdjust.right() - newWidth); rectAdjust.setTop(rectAdjust.bottom() - newHeight); } } else if (DRAG_TOP_RIGHT == enAction) { //缩放（左下不变） xDiff = ptEvent.x() - m_rectOfRedLine.right(); yDiff = ptEvent.y() - m_rectOfRedLine.y(); rectAdjust.adjust(0, yDiff, xDiff, 0); if (SCALE_FIX == m_eumScaleType) { int newWidth = rectAdjust.width(); int newHeight = newWidth * CAPTURE_HEIGHT / CAPTURE_WIDTH; rectAdjust.setRight(rectAdjust.left() + newWidth); rectAdjust.setTop(rectAdjust.bottom() - newHeight); } } else if (DRAG_BOTTOM_LEFT == enAction) { //缩放（右上不变） xDiff = ptEvent.x() - m_rectOfRedLine.x(); yDiff = ptEvent.y() - m_rectOfRedLine.bottom(); rectAdjust.adjust(xDiff, 0, 0, yDiff); if (SCALE_FIX == m_eumScaleType) { int newWidth = rectAdjust.width(); int newHeight = newWidth * CAPTURE_HEIGHT / CAPTURE_WIDTH; rectAdjust.setLeft(rectAdjust.right() - newWidth); rectAdjust.setBottom(rectAdjust.top() + newHeight); } } else if (DRAG_BOTTOM_RIGHT == enAction) { //缩放（左上不变） xDiff = ptEvent.x() - m_rectOfRedLine.right(); yDiff = ptEvent.y() - m_rectOfRedLine.bottom(); rectAdjust.adjust(0, 0, xDiff, yDiff); if (SCALE_FIX == m_eumScaleType) { int newWidth = rectAdjust.width(); int newHeight = newWidth * CAPTURE_HEIGHT / CAPTURE_WIDTH; rectAdjust.setRight(rectAdjust.left() + newWidth); rectAdjust.setBottom(rectAdjust.top() + newHeight); } }------解决方案--------------------
switch有跳转表 直接可以跳转 效率高 if else得一个一个判断