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std::basic_...eam::putback(3) C++ Standard Libarystd::basic_...eam::putback(3) NAME std::basic_istream::putback - std::basic_istream::putback Synopsis basic_istream& putback( char_type ch ); 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. Parameters ch - character to put into input stream 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 bad- bit is set. If exceptions() is set for badbit, the exception is rethrown. Example demonstrates the difference between modifying and non-modifying put- back() // 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::cout << "--\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(); std::cout << "--\n"; 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 See also sputbackc puts one character back in the input sequence (public member function of std::basic_stream- buf<CharT,Traits>) unget unextracts a character (public member function) peek reads the next character without extracting it (public member function) http://cppreference.com 2022.07.31 std::basic_...eam::putback(3)
NAME | Synopsis | Parameters | Return value | Exceptions | Example | Output: | See also
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