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std::basic_streambuf::sputbackc

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< cpp‎ | io‎ | basic streambuf
Revision as of 09:31, 15 August 2013 by P12 (Talk | contribs)

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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.

Contents

[edit] Parameters

(none)

[edit] 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.

[edit] Example

#include <iostream>
#include <sstream>
 
int main()
{
    std::stringstream s("abcdef"); // gptr() poitns to 'a'
    std::cout << "Before putback, string holds " << s.str() << '\n';
    char c1 = s.get(); // c = 'a', gptr() now points to 'b' 
    char c2 = s.rdbuf()->sputbackc('z'); // same as s.putback('c')
                                         // gptr() now points to 'z'
    std::cout << "After putback, string holds " << s.str() << '\n';
    char c3 = s.get(); // c3 = 'z', gptr() now points to 'b'
    std::cout << c1 << c2 << c3 << '\n';
 
    s.rdbuf()->sputbackc('b');  // back to 'b'
    s.rdbuf()->sputbackc('z');  // back to 'z'
    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
azz
No room to putback after 'z'

[edit] See also

moves the next pointer in the input sequence back by one
(public member function) [edit]
puts character into input stream
(public member function of std::basic_istream) [edit]