std::basic_istream<CharT,Traits>::unget
basic_istream& unget(); |
||
Makes the most recently extracted character available again.
First clears eofbit, then behaves as UnformattedInputFunction. After constructing and checking the sentry object, if any ios_base::iostate flags are set, the function sets failbit and returns. Otherwise, calls rdbuf()->sungetc().
If rdbuf()->sungetc() returns Traits::eof(), calls setstate(badbit).
In any case, sets the gcount() counter to zero.
Parameters
(none)
Return value
*this
Exceptions
failure if an error occurred (the error state flag is not goodbit) and exceptions() is set to throw for that state.
If an internal operation throws an exception, it is caught and badbit is set. If exceptions() is set for badbit, the exception is rethrown.
Example
#include <iostream>
#include <sstream>
int main()
{
std::istringstream s1("Hello, world.");
char c1 = s1.get();
if (s1.unget())
{
char c2 = s1.get();
std::cout << "Got: '" << c1 << "'. Got again: '" << c2 << "'.\n";
}
}
Output:
Got: 'H'. Got again: 'H'.
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 1328 (N3168) |
C++98 | unget doesn't clear eofbit
|
clears eofbit before doing anything else
|
See also
| moves the next pointer in the input sequence back by one (public member function of std::basic_streambuf<CharT,Traits>)
| |
| extracts characters (public member function) | |
| reads the next character without extracting it (public member function) | |
| puts a character into input stream (public member function) |