请问，标准C++类streambuf中的get区的putback区是做什么用的呢？

[0602]

谢谢

[anrxhzh]

putback 用来把从输入流中取出的元素放回去。下面是 The C++ Programming Language 中的例子：

istream& operator>>(istream& s, complex& a)
/*
input formats for a complex("f" indicates a floating-point number):
f
(f)
(f.f)
*/
{
double re=0,im=0;
char c=0;

s >> c;
if(c=='(') {
s>>re>>c;
if(c=='.') s>>im>>c;
if(c!=')') s.clear(ios_base::badit); //set state
}
else {
s.putback(c);
s>>re;
}
if(s) a=complex(re,im);
return s;
}

[anrxhzh]

putback 用来把从输入流中取出的元素放回去。下面是 The C++ Programming Language 中的例子：

istream& operator>>(istream& s, complex& a)
/*
input formats for a complex("f" indicates a floating-point number):
f
(f)
(f.f)
*/
{
double re=0,im=0;
char c=0;

s >> c;
if(c=='(') {
s>>re>>c;
if(c=='.') s>>im>>c;
if(c!=')') s.clear(ios_base::badit); //set state
}
else {
s.putback(c);
s>>re;
}
if(s) a=complex(re,im);
return s;
}