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std::basic_filebuf::seekoff

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< cpp‎ | io‎ | basic filebuf

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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_filebuf
Funzioni membro pubbliche
Original:
Public member functions
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basic_filebuf::basic_filebuf
basic_filebuf::~basic_filebuf
basic_filebuf::operator=(C++11)
basic_filebuf::swap(C++11)
basic_filebuf::is_open
basic_filebuf::open
basic_filebuf::close
Protetto funzioni membro
Original:
Protected member functions
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basic_filebuf::showmanyc
basic_filebuf::underflow
basic_filebuf::uflow
basic_filebuf::pbackfail
basic_filebuf::overflow
basic_filebuf::setbuf
basic_filebuf::seekoff
basic_filebuf::seekpos
basic_filebuf::sync
basic_filebuf::imbue
Non membri funzioni
Original:
Non-member functions
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swap(std::basic_filebuf)(C++11)
 
protected:

virtual pos_type seekoff( off_type off,
                          std::ios_base::seekdir way,

                          std::ios_base::openmode which = std::ios_base::in | std::ios_base::out );
Riposiziona il puntatore del file, se possibile, nella posizione che corrisponde esattamente a off caratteri all'inizio, alla fine o la posizione corrente del file (a seconda del valore di way.
Original:
Repositions the file pointer, if possible, to the position that corresponds to exactly off characters from beginning, end, or current position of the file (depending on the value of way.
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Se il file associato non è aperto (is_open()==false, non riesce immediatamente.
Original:
If the associated file is not open (is_open()==false, fails immediately.
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Se la codifica dei caratteri multibyte è dipendente dallo stato (codecvt::encoding() restituito -1) o di lunghezza variabile (codecvt::encoding() restituito ​0​) e il off offset non è ​0​, non riesce subito:. questa funzione non è possibile determinare il numero di byte che corrispondono a off caratteri.
Original:
If the multibyte character encoding is state-dependent (codecvt::encoding() returned -1) or variable-length (codecvt::encoding() returned ​0​) and the offset off is not ​0​, fails immediately: this function cannot determine the number of bytes that correspond to off characters.
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Se way non è std::basic_ios::cur o il off offset non è ​0​, e il più risentono operazione fatta su questo oggetto filebuf era uscita (vale a dire, sia il buffer messo non è vuoto, o la funzione più recente è stata chiamata overflow()), quindi chiama std::codecvt::unshift per determinare la sequenza unshift necessario, e scrive che la sequenza nel file chiamando overflow().
Original:
If way is not std::basic_ios::cur or the offset off is not ​0​, and the most resent operation done on this filebuf object was output (that is, either the put buffer is not empty, or the most recently called function was overflow()), then calls std::codecvt::unshift to determine the unshift sequence necessary, and writes that sequence to the file by calling overflow().
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converte Poi il way argomento a un valore di whence int natura è la seguente:..
Original:
Then converts the argument way to a value whence of type int as follows:
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valore di way
Original:
value of way
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 value of whence
std::basic_ios::beg SEEK_SET
std::basic_ios::end SEEK_END
std::basic_ios::cur SEEK_CUR
Poi, se il carattere codifica è a larghezza fissa (codecvt::encoding() restituisce un po 'di width numero positivo, si sposta il puntatore del file come per std::fseek(file, width*off, whence).
Original:
Then, if the character encoding is fixed-width (codecvt::encoding() returns some positive number width, moves the file pointer as if by std::fseek(file, width*off, whence).
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caso contrario, si muove il puntatore del file come per std::fseek(file, 0, whence).
Original:
Otherwise, moves the file pointer as if by std::fseek(file, 0, whence).
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L'argomento openmode, richiesto dalla firma della funzione della classe base , di solito è ignorata, perché std::basic_filebuf mantiene solo una posizione del file.
Original:
The openmode argument, required by the base class function signature, is usually ignored, because std::basic_filebuf maintains only one file position.
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Indice

[modifica] Parametri

off -
posizione relativa per impostare l'indicatore di posizione di .
Original:
relative position to set the position indicator to.
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dir -
definisce la posizione di base per applicare l'offset rispetto. Essa può essere una delle seguenti costanti:
Constant
Original:
Constant
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 Explanation
beg
l'inizio di un flusso
Original:
the beginning of a stream
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end
la fine di un corso d'acqua
Original:
the ending of a stream
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cur
la posizione corrente del flusso di indicatore di posizione
Original:
the current position of stream position indicator
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Original:
defines base position to apply the relative offset to. It can be one of the following constants:
Constant
Original:
Constant
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 Explanation
beg
l'inizio di un flusso
Original:
the beginning of a stream
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end
la fine di un corso d'acqua
Original:
the ending of a stream
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cur
la posizione corrente del flusso di indicatore di posizione
Original:
the current position of stream position indicator
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which -
che definisce dell'ingresso e / o sequenze di uscita per incidere. Essa può essere una o una combinazione delle seguenti costanti:
Constant
Original:
Constant
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 Explanation
in
influenzano la sequenza di ingresso
Original:
affect the input sequence
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out
influenzano la sequenza di uscita
Original:
affect the output sequence
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Original:
defines which of the input and/or output sequences to affect. It can be one or a combination of the following constants:
Constant
Original:
Constant
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 Explanation
in
influenzano la sequenza di ingresso
Original:
affect the input sequence
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out
influenzano la sequenza di uscita
Original:
affect the output sequence
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[modifica] Valore di ritorno

Un oggetto di nuova costruzione di pos_type tipo che memorizza la posizione di file risultante, o in caso di fallimento.. pos_type(off_type(-1))
Original:
A newly constructed object of type pos_type which stores the resulting file position, or pos_type(off_type(-1)) on failure.
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[modifica] Note

seekoff() è chiamato da std::basic_streambuf::pubseekoff, che è chiamato da std::basic_istream::seekg, std::basic_ostream::seekp, std::basic_istream::tellg e std::basic_ostream::tellp
Original:
seekoff() is called by std::basic_streambuf::pubseekoff, which is called by std::basic_istream::seekg, std::basic_ostream::seekp, std::basic_istream::tellg, and std::basic_ostream::tellp
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[modifica] Esempio

#include <iostream>
#include <fstream>
#include <locale>
int main()
{
    // prepare a 10-byte file holding 4 characters in UTF8
    std::ofstream("text.txt") << u8"z\u00df\u6c34\U0001d10b"; // or u8"zß水𝄋"
                                           // or "\x7a\xc3\x9f\xe6\xb0\xb4\xf0\x9d\x84\x8b";
 
    // open using a non-converting encoding
    std::ifstream f1("text.txt");
    std::cout << "f1's locale's encoding() returns "
              << std::use_facet<std::codecvt<char, char, std::mbstate_t>>(f1.getloc()).encoding() << '\n'
              << "pubseekoff(3, beg) returns " << f1.rdbuf()->pubseekoff(3, std::ios_base::beg) << '\n'
              << "pubseekoff(0, end) returns " << f1.rdbuf()->pubseekoff(0, std::ios_base::end) << '\n';;
 
    // open using UTF-8
    std::wifstream f2("text.txt");
    f2.imbue(std::locale("en_US.UTF-8"));
    std::cout << "f2's locale's encoding() returns "
              << std::use_facet<std::codecvt<wchar_t, char, std::mbstate_t>>(f2.getloc()).encoding() << '\n'
              << "pubseekoff(3, beg) returns " << f2.rdbuf()->pubseekoff(3, std::ios_base::beg) << '\n'
              << "pubseekoff(0, end) returns " << f2.rdbuf()->pubseekoff(0, std::ios_base::end) << '\n';
 
}

Output: 

f1's locale's encoding() returns 1
pubseekoff(3, beg) returns 3
pubseekoff(0, end) returns 10
f2's locale's encoding() returns 0
pubseekoff(3, beg) returns -1
pubseekoff(0, end) returns 10

[modifica] Vedi anche
Invoca seekoff()
Original:
invokes seekoff()
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(metodo pubblico) [modifica]
[virtuale]
riposiziona la posizione del file, usando l'indirizzamento assoluto
Original:
repositions the file position, using absolute addressing
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(virtuale protetto funzione membro) [modifica]
si sposta l'indicatore di posizione file in una posizione specifica in un file
Original:
moves the file position indicator to a specific location in a file
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(funzione) [modifica]
Estratto da "https://it.cppreference.com/mwiki/index.php?title=cpp/io/basic_filebuf/seekoff&oldid=25616"