From cppreference.com
int_typesungetc();If a putback position is available in the get area (gptr()>eback()), then decrements the next pointer (
) and returns the character it now points to.
If a putback position is not available, then calls
to back up the input sequence if possible.
The I/O stream function
is implemented in terms of this function.
Parameters
(none)
Return value
If putback position was available, returns the character that the next pointer is now pointing at, converted to int_type with Traits::to_int_type(*gptr()). The next single-character input from this streambuf will return this character.
If putback position was not available, returns what
returns, which is Traits::eof() on failure.
Example
Run this code
#include<iostream>#include<sstream>intmain(){std::stringstreams("abcdef");// gptr() points to 'a'charc1=s.get();// c = 'a', gptr() now points to 'b' charc2=s.rdbuf()->sungetc();// same as s.unget(): gptr() points to 'a' again charc3=s.get();// c3 = 'a', gptr() now points to 'b'charc4=s.get();// c4 = 'b', gptr() now points to 'c'std::cout<<c1<<c2<<c3<<c4<<'\n';s.rdbuf()->sungetc();// back to 'b's.rdbuf()->sungetc();// back to 'a'inteof=s.rdbuf()->sungetc();// nothing to unget: pbackfail() failsif(eof==EOF)std::cout<<"Nothing to unget after 'a'\n";}Output:
aaab Nothing to unget after 'a' See also
puts one character back in the input sequence
(public member function)
unextracts a character
(public member function of std::basic_istream<CharT,Traits>)