std::basic_streambuf::sputbackc - cppreference.com

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# std::basic_streambuf::sputbackc

From cppreference.com
< cpp‎ | io‎ | basic streambuf

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.

### [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

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'

### [edit] See also

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

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