怎么设置X,Y轴位置
Manages a single axis inside a QCustomPlot.
Usually doesn't need to be instantiated externally. Access QCustomPlot's default four axes via QCustomPlot::xAxis (bottom), QCustomPlot::yAxis (left), QCustomPlot::xAxis2 (top) and QCustomPlot::yAxis2 (right).
Axes are always part of an axis rect, see QCPAxisRect.
