MATLAB 中gcf、gca 以及gco 的区别

gcf 返回当前Figure 对象的句柄值 gca 返回当前axes 对象的句柄值 gco 返回当前鼠标单击的句柄值，该对象可以是除root 对象外的任意图形对象，并且Matlab 会把当前图形对象的句柄值存放在Figure 的CurrentObject属性中。 

function h=gcf() % GCF Get current figure handle. % H=GCF returns the handle to the current figure.The current fugure is the figure(graphics window)that graphics commands like PLOT,TITLE,SURF,etc.draw to if issued. % % Use the commands FIGURE to change the current figure to a diffent figure,or to create new % ones. % % See also FIGURE,CLOSE,CLF,GCA. % Copyright (c) 1984-94 by The MathWorks,Inc. h=get(0, 'CurrentFigure' ); 
类似的，函数gca 返回当前图形的 'CurrentAxes' 属性值，它的M 文件描 述如下。 
function h=gca() % GCA Get current axis handle. % H=GCA returns the handle to the current axis.The current axis is the axis that graphics % command like PLOT,TITLE,SURF,etc.draw to if issued. % % Use the commands AXES or SUBPLOT to change the current axis to a different axis,or to % create new ones. % see also AXES,SUBPLOT,DELETE,CLA,HOLD,GCF. % Copyright (c) 1984-94 by The MathWorks,Inc.h=get(get(0, 'CurrentFigure' ), 'CurrentAxes' ); 
函数gco 也相同，只是它在试图获得当前对象之前先检查图形是否存在。注意函数gcf 和gca 能促使建立相关的对象，如果它们不存在的话。如下所示的函数gco，它先检查子对象（ 'Children' ）是否存在，如果不存在，就不创建图形对象。 
function object=gco(figure) 
%GCO Handle of current object. % OBJECT=GCO returns the current object in the current figure. % % OBJECT=GCO(FIGURE) returns the current object in figure FIGURE. % % The current object for a given figure is the last object clicked on with mouse. %Copyright (c) 1984-94 by The MathWorks,Inc. 
if isempty(get(0, 'Children' )) object=[ ]; return; end; if (nargin==0) figure=get(0, 'CurrentFigure' ); end object=get(figure, 'CurrentObject' ); 当需要一些除了 'CurrentFigure' 、 'CurrentAxes' 和 'CurrentObject' 之外的某些东西时，可以用函数get 来获得一个对象的子对象的句柄向量。例如： Hx_kids=get(gcf, 'Children' )返回一个向量，它包含当前图形子对象的句柄。 可以用获得子对象 'Children' 句柄的技术彻底搜索句柄图形的层次结构中来找到所要的对象。例如，在画出一些数据后，寻找绿色线条句柄的问题。 x=-pi:pi/20:pi; % create some data y=sin(x); z=cos(x); plot(x,y, 'r' ,x,z, 'g' ); % plot two lines in red and green Hl_lines=get(gca, 'Children' ); % get the line handles for k=1:size(Hl_lines) % find the green line if get(Hl_lines(k), 'Color' )==[0 1 0] Hl_green=Hl_lines(k) end end Hl_green= 58.0001