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std::basic_istream::putback

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< cpp‎ | io‎ | basic istream

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C++
 
Ingresso / libreria di output
I / O manipolatori
C-style I / O
Buffer
Original:
Buffers
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basic_streambuf
basic_filebuf
basic_stringbuf
strstreambuf(deprecato)
Streams
Original:
Streams
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Astrazioni
Original:
Abstractions
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ios_base
basic_ios
basic_istream
basic_ostream
basic_iostream
File I / O
Original:
File I/O
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basic_ifstream
basic_ofstream
basic_fstream
String I / O
Original:
String I/O
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basic_istringstream
basic_ostringstream
basic_stringstream
Array I / O
Original:
Array I/O
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istrstream(deprecato)
ostrstream(deprecato)
strstream(deprecato)
Tipi
Original:
Types
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streamoff
streamsize
fpos
Errore categoria interfaccia
Original:
Error category interface
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iostream_category(C++11)
io_errc(C++11)
 
std::basic_istream
Gli oggetti globali
Original:
Global objects
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cin
wcin
Membri funzioni
Original:
Member functions
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basic_istream::basic_istream
basic_istream::~basic_istream
basic_istream::operator=(C++11)
Ingresso formattato
Original:
Formatted input
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basic_istream::operator>>
Ingresso non formattato
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Unformatted input
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basic_istream::get
basic_istream::peek
basic_istream::unget
basic_istream::putback
basic_istream::getline
basic_istream::ignore
basic_istream::read
basic_istream::readsome
basic_istream::gcount
Posizionamento
Original:
Positioning
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basic_istream::tellg
basic_istream::seekg
Varie
Original:
Miscellaneous
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basic_istream::sync
basic_istream::swap(C++11)
Membri classi
Original:
Member classes
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basic_istream::sentry
Non membri funzioni
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Non-member functions
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operator>>(std::basic_istream)
 
basic_istream& putback( char_type ch );
Inserisce il carattere ch torna il flusso di input in modo che il carattere successivo estratto sarà ch.
Original:
Puts the character ch back to the input stream so the next extracted character will be ch.
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In primo luogo cancella eofbit, quindi si comporta come UnformattedInputFunction. Dopo la costruzione e la verifica dell'oggetto sentinella, se rdbuf() non è nullo, chiama rdbuf()->sputbackc(ch), che chiama rdbuf()->pbackfail(ch) ch se non è uguale al personaggio più recente estratto.
Original:
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.
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Se rdbuf() è null o se rdbuf->sputbackc(ch) ritorna Traits::eof(), chiama setstate(badbit).
Original:
If rdbuf() is null or if rdbuf->sputbackc(ch) returns Traits::eof(), calls setstate(badbit).
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In ogni caso, imposta il contatore a zero gcount().
Original:
In any case, sets the gcount() counter to zero.
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Indice

[modifica] Parametri

(Nessuno)
Original:
(none)
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[modifica] Valore di ritorno

*this

[modifica] Esempio

illustra la differenza tra la modifica e non modifica putback ()
Original:
demonstrates the difference between modifying and non-modifying putback()
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#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

[modifica] Vedi anche
unextracts un carattere
Original:
unextracts a character
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(metodo pubblico) [modifica]
legge il carattere successivo senza estrarlo
Original:
reads the next character without extracting it
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(metodo pubblico) [modifica]
Estratto da "https://it.cppreference.com/mwiki/index.php?title=cpp/io/basic_istream/putback&oldid=25679"