解析C++浮点数的格式化显示

   #include<stdlib.h> 
   #include<string> 
   #include<windows.h> 
   #include<stdio.h> 
   #include<iostream> 
   #include<limits> 
   #include<sstream> 
   usingnamespacestd; 

   stringdo_fraction(longdoubleval,intdecplaces=3) 
   { 
       ostringstream out; 
       charDECIMAL_POINT=".";//欧洲用法为"," 
       intprec=numeric_limits<longdouble>::digits10;//18 
       out.precision(prec);//覆盖默认精度 
       out<<val; 
       stringstr=out.str();//从流中取出字符串 
       size_tn=str.find(DECIMAL_POINT); 
       if((n!=string::npos)//有小数点吗？ 
           &&(str.size()>n+decplaces))//后面至少还有decplaces位吗？ 
       { 
           str[n+decplaces]="\0";//覆盖第一个多余的数 
       } 
       str.swap(string(str.c_str()));//删除nul之后的多余字符 

       returnstr; 
   }