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std::basic_streambuf::sungetc

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< cpp‎ | io‎ | basic streambuf
Revision as of 09:09, 27 June 2013 by SuperBoi45 (Talk | contribs)

 
 
 
 
int_type sungetc();

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

If a putback position is not available, then calls Template:rlpf to back up the input sequence if possible.

The I/O stream function basic_istream::unget is implemented in terms of this function.

Contents

Parameters

(none)

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

Example

#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'

See also

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