std::basic_streambuf::sputbackc
性病：基本[医]流f：：sputbackc
| int_type sputbackc( char_type c | | |
|---|
将字符返回到GET区域。
如果在GET区域%28中有一个备用位置gptr() > eback()%29，和字符c的左边的一个位置等于字符。gptr()28%Traits::eq(c, gptr()[-1])，然后简单地减少下一个指针%28gptr()29%。
否则，打电话pbackfail(Traits::to_int_type(c))要么备份GET区域，要么修改GET区域，并可能修改相关的字符序列。
I/O流函数basic_istream::putback是根据此功能实现的。
参数
%280%29
返回值
如果返回位置可用，则返回下一个指针指向的字符，转换为int_type带着Traits::to_int_type(*gptr())下一个单字符输入将返回这个字符。
如果没有备用位置，则返回pbackfail()返回，即Traits::eof()在失败的时候。
例
二次
#include <iostream>
#include <sstream>
int main()
{
std::stringstream s("abcdef" // gptr() points to 'a' in "abcdef"
std::cout << "Before putback, string holds " << s.str() << '\n';
char c1 = s.get( // c1 = 'a', gptr() now points to 'b' in "abcdef"
char c2 = s.rdbuf()->sputbackc('z' // same as s.putback('z')
// gptr() now points to 'z' in "zbcdef"
std::cout << "After putback, string holds " << s.str() << '\n';
char c3 = s.get( // c3 = 'z', gptr() now points to 'b' in "zbcdef"
char c4 = s.get( // c4 = 'b', gptr() now points to 'c' in "zbcdef"
std::cout << c1 << c2 << c3 << c4 << '\n';
s.rdbuf()->sputbackc('b' // gptr() now points to 'b' in "zbcdef"
s.rdbuf()->sputbackc('z' // gptr() now points to 'z' in "zbcdef"
int eof = s.rdbuf()->sputbackc('x' // nothing to unget: pbackfail() fails
if (eof == EOF)
std::cout << "No room to putback after 'z'\n";
}
二次
产出：
二次
Before putback, string holds abcdef
After putback, string holds zbcdef
azzb
No room to putback after 'z'
二次
另见
| sungetc | moves the next pointer in the input sequence back by one (public member function) |
|---|---|
| putback | puts character into input stream (public member function of std::basic_istream) |
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