std::basic_istream<CharT,Traits>::putback

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

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

Return value

*this

Exceptions

If an internal operation throws an exception, it is caught and badbit is set. If exceptions() is set for badbit

Example

#include <iostream>
#include <sstream>
 
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";
}

Yello, world
--
putback failed
--
Hello, world

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also