std::basic_fstream
From cppreference.com
| Defined in header <fstream>
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| template< class CharT, |
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The class template basic_fstream implements high-level input/output operations on file based streams. It interfaces a file-based streambuffer (std::basic_filebuf) with the high-level interface of (std::basic_iostream).
A typical implementation of std::basic_fstream holds only one non-derived data member: an instance of std::basic_filebuf<CharT, Traits>.
Inheritance diagram
Several typedefs for common character types are provided:
| Defined in header
<fstream> | |
| Type | Definition |
std::fstream
|
std::basic_fstream<char> |
std::wfstream
|
std::basic_fstream<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 |
native_handle_type(C++26)
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implementation-defined type that is TriviallyCopyable and semiregular |
Member functions
| constructs the file stream (public member function) | |
| (destructor) [virtual] (implicitly declared) |
destructs the basic_fstream and the associated buffer, closes the file (virtual public member function) |
| (C++11) |
moves the file stream (public member function) |
| (C++11) |
swaps two file streams (public member function) |
| returns the underlying raw file device object (public member function) | |
| (C++26) |
returns the underlying implementation-defined handle (public member function) |
File operations | |
| checks if the stream has an associated file (public member function) | |
| opens a file and associates it with the stream (public member function) | |
| closes the associated file (public member function) | |
Non-member functions
| specializes the std::swap algorithm (function template) |
Inherited from std::basic_istream
Member functions
Formatted input | |
| extracts formatted data (public member function of std::basic_istream<CharT,Traits>) | |
Unformatted input | |
| extracts characters (public member function of std::basic_istream<CharT,Traits>) | |
| reads the next character without extracting it (public member function of std::basic_istream<CharT,Traits>) | |
| unextracts a character (public member function of std::basic_istream<CharT,Traits>) | |
| puts a character into input stream (public member function of std::basic_istream<CharT,Traits>) | |
| extracts characters until the given character is found (public member function of std::basic_istream<CharT,Traits>) | |
| extracts and discards characters until the given character is found (public member function of std::basic_istream<CharT,Traits>) | |
| extracts blocks of characters (public member function of std::basic_istream<CharT,Traits>) | |
| extracts already available blocks of characters (public member function of std::basic_istream<CharT,Traits>) | |
| returns number of characters extracted by last unformatted input operation (public member function of std::basic_istream<CharT,Traits>) | |
Positioning | |
| returns the input position indicator (public member function of std::basic_istream<CharT,Traits>) | |
| sets the input position indicator (public member function of std::basic_istream<CharT,Traits>) | |
Miscellaneous | |
| synchronizes with the underlying storage device (public member function of std::basic_istream<CharT,Traits>) | |
Member classes
| implements basic logic for preparation of the stream for input operations (public member class of std::basic_istream<CharT,Traits>) |
Inherited from std::basic_ostream
Member functions
Formatted output | |
| inserts formatted data (public member function of std::basic_ostream<CharT,Traits>) | |
Unformatted output | |
| inserts a character (public member function of std::basic_ostream<CharT,Traits>) | |
| inserts blocks of characters (public member function of std::basic_ostream<CharT,Traits>) | |
Positioning | |
| returns the output position indicator (public member function of std::basic_ostream<CharT,Traits>) | |
| sets the output position indicator (public member function of std::basic_ostream<CharT,Traits>) | |
Miscellaneous | |
| synchronizes with the underlying storage device (public member function of std::basic_ostream<CharT,Traits>) | |
Member classes
| implements basic logic for preparation of the stream for output operations (public member class of std::basic_ostream<CharT,Traits>) |
Inherited from std::basic_ios
Member types
| Member type | Definition |
char_type
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CharT
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traits_type
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Traits
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int_type
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Traits::int_type
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pos_type
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Traits::pos_type
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off_type
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Traits::off_type
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Member functions
State functions | |
| checks if no error has occurred i.e. I/O operations are available (public member function of std::basic_ios<CharT,Traits>) | |
| checks if end-of-file has been reached (public member function of std::basic_ios<CharT,Traits>) | |
| checks if an error has occurred (public member function of std::basic_ios<CharT,Traits>) | |
| checks if a non-recoverable error has occurred (public member function of std::basic_ios<CharT,Traits>) | |
| checks if an error has occurred (synonym of fail()) (public member function of std::basic_ios<CharT,Traits>) | |
checks if no error has occurred (synonym of !fail()) (public member function of std::basic_ios<CharT,Traits>) | |
| returns state flags (public member function of std::basic_ios<CharT,Traits>) | |
| sets state flags (public member function of std::basic_ios<CharT,Traits>) | |
| modifies state flags (public member function of std::basic_ios<CharT,Traits>) | |
Formatting | |
| copies formatting information (public member function of std::basic_ios<CharT,Traits>) | |
| manages the fill character (public member function of std::basic_ios<CharT,Traits>) | |
Miscellaneous | |
| manages exception mask (public member function of std::basic_ios<CharT,Traits>) | |
| sets the locale (public member function of std::basic_ios<CharT,Traits>) | |
| manages associated stream buffer (public member function of std::basic_ios<CharT,Traits>) | |
| manages tied stream (public member function of std::basic_ios<CharT,Traits>) | |
| narrows characters (public member function of std::basic_ios<CharT,Traits>) | |
| widens characters (public member function of std::basic_ios<CharT,Traits>) | |
Inherited from std::ios_base
Member functions
Formatting | |
| manages format flags (public member function of std::ios_base) | |
| sets specific format flag (public member function of std::ios_base) | |
| clears specific format flag (public member function of std::ios_base) | |
| manages decimal precision of floating point operations (public member function of std::ios_base) | |
| manages field width (public member function of std::ios_base) | |
Locales | |
| sets locale (public member function of std::ios_base) | |
| returns current locale (public member function of std::ios_base) | |
Internal extensible array | |
| [static] |
returns a program-wide unique integer that is safe to use as index to pword() and iword() (public static member function of std::ios_base) |
| resizes the private storage if necessary and access to the long element at the given index (public member function of std::ios_base) | |
| resizes the private storage if necessary and access to the void* element at the given index (public member function of std::ios_base) | |
Miscellaneous | |
| registers event callback function (public member function of std::ios_base) | |
| [static] |
sets whether C++ and C I/O libraries are interoperable (public static member function of std::ios_base) |
Member classes | |
| stream exception (public member class of std::ios_base) | |
| 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:
(typedef) | |||||||||||||||||||||||||||||||||||||||
| formatting flags type
The following constants are also defined:
(typedef) | |||||||||||||||||||||||||||||||||||||||
| state of the stream type
The following constants are also defined:
(typedef) | |||||||||||||||||||||||||||||||||||||||
| seeking direction type
The following constants are also defined:
(typedef) | |||||||||||||||||||||||||||||||||||||||
| specifies event type (enum) | |||||||||||||||||||||||||||||||||||||||
| callback function type (typedef) | |||||||||||||||||||||||||||||||||||||||
Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_fstream_native_handle |
202306L |
(C++26) | native handles support |
Example
Run this code
#include <fstream> #include <iostream> #include <string> int main() { std::string filename{"test.bin"}; std::fstream s{filename, s.binary | s.trunc | s.in | s.out}; if (!s.is_open()) std::cout << "failed to open " << filename << '\n'; else { // write double d{3.14}; s.write(reinterpret_cast<char*>(&d), sizeof d); // binary output s << 123 << "abc"; // text output // for fstream, this moves the file position pointer (both put and get) s.seekp(0); // read d = 2.71828; s.read(reinterpret_cast<char*>(&d), sizeof d); // binary input int n; std::string str; if (s >> n >> str) // text input std::cout << "read back from file: " << d << ' ' << n << ' ' << str << '\n'; } }
Output:
read back from file: 3.14 123 abc
See also
| read data from an I/O stream into a string (function template) |