[xiezhh]

如下测试没有问题

fig = figure ;
set(fig,'units','normalized','position',[0.0381 0.0742 0.9277 0.8464],...
'menubar','none','name','成绩分析系统',...
'numbertitle','off','color',[0.925 0.914 0.847],'tag','cjfx');
panel0=uipanel(fig,'units','normalized','pos',[0.038 0.002 0.646 0.265],'title','请输入相关信息',...
'fontsize',12,'fontweight','bold');
panel0=uipanel(fig,'units','normalized','pos',[0.038 0.002 0.646 0.265],'title','请输入相关信息',...
'fontsize',12,'fontweight','bold');
uicontrol(panel0,'style','edit','units','normalized','pos',[0.55 0.74 0.15 0.22],...
'fontsize',14,'fontunits','normalized','tag','edit1','backgroundcolor',[1 1 1]);
h=findobj(gcf,'tag','edit1');

user_entry=str2double(get(h,'String'));
if isempty(user_entry)
user_entry=0;
else
a=user_entry;
end

需要注意的是，若编辑框不输任何字符，user_entry=str2double(get(h,'String'));返回的user_entry为NaN，不为空。