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

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

NAME

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

Synopsis

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.

Parameters

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.

Example

// 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";
  }

Output:

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