std::basic_streambuf::sungetc - cppreference.com

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# std::basic_streambuf::sungetc

From cppreference.com
< cpp‎ | io‎ | basic streambuf

int_type sungetc(); |  |

If a putback position is available in the get area (gptr() > eback()), then decrements the next pointer (gptr()) and returns the character it now points to.

If a putback position is not available, then calls pbackfail() to back up the input sequence if possible.

The I/O stream function `basic_istream::unget` 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() poitns to 'a'
        char c1 = s.get(); // c = 'a', gptr() now points to 'b'
        char c2 = s.rdbuf()->sungetc(); // same as s.unget(): gptr() points to 'a' again
        char c3 = s.get(); // c3 = 'a', gptr() now points to 'b'
        char c4 = 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'
        int eof = s.rdbuf()->sungetc();  // nothing to unget: pbackfail() fails
        if (eof == EOF)
                std::cout << "Nothing to unget after 'a'\n";
    }

Output:

    aaab
    Nothing to unget after 'a'

### [edit] See also

sputbackc | puts one character back in the input sequence (public member function) [edit]
unget | unextracts a character (public member function of `std::basic_istream`) [edit]

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