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.
(none).
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.
#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'
puts one character back in the input sequence (public member function) |
|
unextracts a character (public member function of std::basic_istream<CharT,Traits> ) |
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