std::basic_streambuf::sungetc
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< 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.
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[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
| puts one character back in the input sequence (public member function) | |
| unextracts a character (public member function of std::basic_istream)
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