std::basic_istream::putback
From cppreference.com
< cpp | io | basic istream
| basic_istream& putback( char_type ch );
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Puts the character ch back to the input stream so the next extracted character will be ch.
First clears eofbit, then behaves as UnformattedInputFunction. After constructing and checking the sentry object, if rdbuf() is not null, calls rdbuf()->sputbackc(ch), which calls rdbuf()->pbackfail(ch) if ch does not equal the most recently extracted character.
If rdbuf() is null or if rdbuf->sputbackc(ch) returns Traits::eof(), calls setstate(badbit).
In any case, sets the gcount() counter to zero.
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[edit] Parameters
| ch | - | character to put into input stream |
[edit] Return value
*this
[edit] Exceptions
If an internal operation throws an exception, it is caught and badbit is set. If exceptions() is set for badbit, the exception is rethrown.
[edit] Example
demonstrates the difference between modifying and non-modifying putback()
Run this code
#include <sstream> #include <iostream> int main() { std::stringstream s1("Hello, world"); // IO stream s1.get(); if (s1.putback('Y')) // modifies the buffer std::cout << s1.rdbuf() << '\n'; else std::cout << "putback failed\n"; std::istringstream s2("Hello, world"); // input-only stream s2.get(); if (s2.putback('Y')) // cannot modify input-only buffer std::cout << s2.rdbuf() << '\n'; else std::cout << "putback failed\n"; s2.clear(); if (s2.putback('H')) // non-modifying putback std::cout << s2.rdbuf() << '\n'; else std::cout << "putback failed\n"; }
Output:
Yello, world putback failed Hello, world
[edit] See also
| puts one character back in the input sequence (public member function of std::basic_streambuf)
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| unextracts a character (public member function) |
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| reads the next character without extracting it (public member function) |