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std::basic_ifstream(3) C++ Standard Libary std::basic_ifstream(3) NAME std::basic_ifstream - std::basic_ifstream Synopsis Defined in header <fstream> template< class CharT, class Traits = std::char_traits<CharT> > class basic_ifstream : public std::basic_istream<CharT, Traits> The class template basic_ifstream implements high-level input opera- tions on file-based streams. It interfaces a file-based streambuffer (std::basic_filebuf) with the high-level interface of (std::basic_istream). A typical implementation of std::basic_ifstream holds only one non- derived data member: an instance of std::basic_filebuf<CharT, Traits>. std-basic ifstream-inheritance.svg Inheritance diagram Two specializations for common character types are also defined: Defined in header <fstream> Type Definition ifstream basic_ifstream<char> wifstream basic_ifstream<wchar_t> Member types Member type Definition char_type CharT traits_type Traits; the program is ill-formed if Traits::char_type is not CharT. int_type Traits::int_type pos_type Traits::pos_type off_type Traits::off_type Member functions constructor constructs the file stream (public member function) destructor destructs the basic_ifstream and the associated [virtual] (implicitly declared) buffer, closes the file (virtual public member function) operator= moves the file stream (C++11) (public member function) swap swaps two file streams (C++11) (public member function) rdbuf returns the underlying raw file de- vice object (public member function) File operations is_open checks if the stream has an associ- ated file (public member function) open opens a file and associates it with the stream (public member function) close closes the associated file (public member function) Non-member functions std::swap(std::basic_ifstream) specializes the std::swap algorithm (C++11) (function template) Inherited from std::basic_istream Member functions Formatted input operator>> extracts formatted data (public member function of std::ba- sic_istream<CharT,Traits>) Unformatted input get extracts characters (public member function of std::ba- sic_istream<CharT,Traits>) peek reads the next character without extracting it (public member function of std::ba- sic_istream<CharT,Traits>) unget unextracts a character (public member function of std::ba- sic_istream<CharT,Traits>) putback puts character into input stream (public member function of std::ba- sic_istream<CharT,Traits>) getline extracts characters until the given character is found (public member function of std::ba- sic_istream<CharT,Traits>) ignore extracts and discards characters until the given charac- ter is found (public member function of std::ba- sic_istream<CharT,Traits>) read extracts blocks of characters (public member function of std::ba- sic_istream<CharT,Traits>) readsome extracts already available blocks of characters (public member function of std::ba- sic_istream<CharT,Traits>) returns number of characters extracted by last unformat- ted input gcount operation (public member function of std::ba- sic_istream<CharT,Traits>) Positioning tellg returns the input position indicator (public member function of std::ba- sic_istream<CharT,Traits>) seekg sets the input position indicator (public member function of std::ba- sic_istream<CharT,Traits>) Miscellaneous sync synchronizes with the underlying storage device (public member function of std::ba- sic_istream<CharT,Traits>) Member classes sentry implements basic logic for preparation of the stream for in- put operations (public member class of std::basic_istream<CharT,Traits>) Inherited from std::basic_ios Member types Member type Definition char_type CharT traits_type Traits int_type Traits::int_type pos_type Traits::pos_type off_type Traits::off_type Member functions State functions good checks if no error has occurred i.e. I/O operations are available (public member function of std::ba- sic_ios<CharT,Traits>) eof checks if end-of-file has been reached (public member function of std::ba- sic_ios<CharT,Traits>) fail checks if an error has occurred (public member function of std::ba- sic_ios<CharT,Traits>) bad checks if a non-recoverable error has occurred (public member function of std::ba- sic_ios<CharT,Traits>) operator! checks if an error has occurred (synonym of fail()) (public member function of std::ba- sic_ios<CharT,Traits>) operator void* operator bool checks if no error has occurred (synonym of !fail()) (until C++11) (public member function of std::ba- sic_ios<CharT,Traits>) (since C++11) rdstate returns state flags (public member function of std::ba- sic_ios<CharT,Traits>) setstate sets state flags (public member function of std::ba- sic_ios<CharT,Traits>) clear modifies state flags (public member function of std::ba- sic_ios<CharT,Traits>) Formatting copyfmt copies formatting information (public member function of std::ba- sic_ios<CharT,Traits>) fill manages the fill character (public member function of std::ba- sic_ios<CharT,Traits>) Miscellaneous exceptions manages exception mask (public member function of std::ba- sic_ios<CharT,Traits>) imbue sets the locale (public member function of std::ba- sic_ios<CharT,Traits>) rdbuf manages associated stream buffer (public member function of std::ba- sic_ios<CharT,Traits>) tie manages tied stream (public member function of std::ba- sic_ios<CharT,Traits>) narrow narrows characters (public member function of std::ba- sic_ios<CharT,Traits>) widen widens characters (public member function of std::ba- sic_ios<CharT,Traits>) Inherited from std::ios_base Member functions Formatting flags manages format flags (public member function of std::ios_base) setf sets specific format flag (public member function of std::ios_base) unsetf clears specific format flag (public member function of std::ios_base) precision manages decimal precision of floating point opera- tions (public member function of std::ios_base) width manages field width (public member function of std::ios_base) Locales imbue sets locale (public member function of std::ios_base) getloc returns current locale (public member function of std::ios_base) Internal extensible array xalloc returns a program-wide unique integer that is safe to use as index [static] to pword() and iword() (public static member function of std::ios_base) resizes the private storage if necessary and ac- cess to the long iword element at the given index (public member function of std::ios_base) resizes the private storage if necessary and ac- cess to the void* pword element at the given index (public member function of std::ios_base) Miscellaneous register_callback registers event callback function (public member function of std::ios_base) sync_with_stdio sets whether C++ and C I/O libraries are interop- erable [static] (public static member function of std::ios_base) Member classes failure stream exception (public member class of std::ios_base) Init initializes standard stream objects (public member class of std::ios_base) Member types and constants Type Explanation stream open mode type The following constants are also defined: Constant Explanation app seek to the end of stream before each write openmode binary open in binary mode in open for reading out open for writing trunc discard the contents of the stream when opening ate seek to the end of stream immediately after open (typedef) formatting flags type The following constants are also defined: Constant Explanation dec use decimal base for integer I/O: see std::dec oct use octal base for integer I/O: see std::oct hex use hexadecimal base for integer I/O: see std::hex basefield dec|oct|hex. Useful for masking opera- tions left left adjustment (adds fill characters to the right): see std::left right right adjustment (adds fill characters to the left): see std::right internal internal adjustment (adds fill characters to the internal designated point): see std::internal adjustfield left|right|internal. Useful for masking operations generate floating point types using sci- entific notation, scientific or hex notation if combined with fixed: see std::scientific fmtflags fixed generate floating point types using fixed notation, or hex notation if combined with scientific: see std::fixed floatfield scientific|fixed. Useful for masking op- erations boolalpha insert and extract bool type in alphanu- meric format: see std::boolalpha generate a prefix indicating the numeric base for integer showbase output, require the currency indicator in monetary I/O: see std::showbase showpoint generate a decimal-point character uncon- ditionally for floating-point number output: see std::showpoint showpos generate a + character for non-negative numeric output: see std::showpos skipws skip leading whitespace before certain input operations: see std::skipws unitbuf flush the output after each output opera- tion: see std::unitbuf replace certain lowercase letters with their uppercase uppercase equivalents in certain output operations: see std::uppercase (typedef) state of the stream type The following constants are also defined: Constant Explanation iostate goodbit no error badbit irrecoverable stream error failbit input/output operation failed (formatting or extraction error) eofbit associated input sequence has reached end- of-file (typedef) seeking direction type The following constants are also defined: seekdir Constant Explanation beg the beginning of a stream end the ending of a stream cur the current position of stream position in- dicator (typedef) event specifies event type (enum) event_callback callback function type (typedef) Example // Run this code #include <iostream> #include <fstream> #include <string> int main() { std::string filename = "Test.b"; // prepare a file to read double d = 3.14; std::ofstream(filename, std::ios::binary).write(reinter- pret_cast<char*>(&d), sizeof d) << 123 << "abc"; // open file for reading std::ifstream istrm(filename, std::ios::binary); if (!istrm.is_open()) { std::cout << "failed to open " << filename << '\n'; } else { double d; istrm.read(reinterpret_cast<char*>(&d), sizeof d); // binary input int n; std::string s; if (istrm >> n >> s) // text input std::cout << "read back from file: " << d << ' ' << n << ' ' << s << '\n'; } } Output: read back from file: 3.14 123 abc http://cppreference.com 2022.07.31 std::basic_ifstream(3)
NAME | Synopsis | Member types | Member functions | File operations | Non-member functions | Member functions | Formatted input | Unformatted input | Positioning | Miscellaneous | Member classes | Member types | Member functions | State functions | Formatting | Miscellaneous | Member functions | Formatting | Locales | Internal extensible array | Miscellaneous | Member classes | Member types and constants | Example | Output:
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