std::basic_streambuf<CharT,Traits>::sungetc - cppreference.com (original) (raw)

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

#include #include   int main() { std::stringstream s("abcdef"); // gptr() points 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

| | puts one character back in the input sequence (public member function) [edit] | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | unextracts a character (public member function of std::basic_istream<CharT,Traits>) [edit] |