std::basic_streambuf<CharT,Traits>::sputbackc (3) - Linux Manuals

std::basic_streambuf<CharT,Traits>::sputbackc: std::basic_streambuf<CharT,Traits>::sputbackc


std::basic_streambuf<CharT,Traits>::sputbackc - std::basic_streambuf<CharT,Traits>::sputbackc


int_type sputbackc( char_type c );

Puts back a character back to the get area.
If a putback position is available in the get area (gptr() > eback()), and the character c is equal to the character one position to the left of gptr() (as determined by Traits::eq(c, gptr()[-1]), then simply decrements the next pointer (gptr()).
Otherwise, calls pbackfail(Traits::to_int_type(c)) to either back up the get area or to modify both the get area and possibly the associated character sequence.
The I/O stream function basic_istream::putback is implemented in terms of this function.


c - character to put back

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 pbackfail() returns, which is Traits::eof() on failure.


// Run this code

  #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";


  Before putback, string holds abcdef
  After putback, string holds zbcdef
  No room to putback after 'z'

See also

        moves the next pointer in the input sequence back by one
sungetc (public member function)
        puts character into input stream
putback (public member function of std::basic_istream<CharT,Traits>)