std::ios_base::openmode

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Input/output library

I/O manipulators

Print functions (C++23)

C-style I/O

Buffers

basic_streambuf

basic_filebuf

basic_stringbuf

basic_spanbuf (C++23)

strstreambuf (C++98/26*)

basic_syncbuf (C++20)

Streams

Abstractions

ios_base

basic_ios

basic_istream

basic_ostream

basic_iostream

File I/O

basic_ifstream

basic_ofstream

basic_fstream

String I/O

basic_istringstream

basic_ostringstream

basic_stringstream

Array I/O

basic_ispanstream (C++23)

basic_ospanstream (C++23)

basic_spanstream (C++23)

istrstream (C++98/26*)

ostrstream (C++98/26*)

strstream (C++98/26*)

Synchronized Output

basic_osyncstream (C++20)

Types

streamoff

streamsize

fpos

Error category interface

iostream_category (C++11)

io_errc (C++11)

 

std::ios_base

Member functions

ios_base::ios_base

ios_base::~ios_base

ios_base::operator=

Formatting

ios_base::flags

ios_base::setf

ios_base::unsetf

ios_base::precision

ios_base::width

Locales

ios_base::imbue

ios_base::getloc

Internal extensible array

ios_base::xalloc

ios_base::iword

ios_base::pword

Miscellaneous

ios_base::register_callback

ios_base::sync_with_stdio

Member classes

ios_base::failure

ios_base::Init

Member types

ios_base::openmode

ios_base::fmtflags

ios_base::iostate

ios_base::seekdir

ios_base::event

ios_base::event_callback

 

typedef /*implementation defined*/ openmode;
static constexpr openmode app       = /*implementation defined*/ static constexpr openmode binary    = /*implementation defined*/ static constexpr openmode in        = /*implementation defined*/ static constexpr openmode out       = /*implementation defined*/ static constexpr openmode trunc     = /*implementation defined*/ static constexpr openmode ate       = /*implementation defined*/
static constexpr openmode noreplace = /*implementation defined*/		(since C++23)

Specifies available file open flags. It is a BitmaskType, the following constants are defined:

Constant	Explanation
app	seek to the end of stream before each write
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
noreplace (C++23)	open in exclusive mode

Example

Run this code

#include <fstream>
#include <iostream>
#include <string>
 
int main()
{
    const char* fname = "unique_name.txt";
 
    // write to a temporary stream object
    std::fstream(fname, std::ios::out | std::ios::trunc) << "Hi";
 
    std::fstream in(fname, std::ios::in);
 
    std::string s;
    in >> s;
    std::cout << s << '\n';
}

Output:

Hi

See also

open	opens a file and configures it as the associated character sequence (public member function of std::basic_filebuf<CharT,Traits>)
(constructor)	constructs a basic_stringbuf object (public member function of std::basic_stringbuf<CharT,Traits,Allocator>)