std::ios_base::openmode

 

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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::string s;
    std::fstream(fname, std::ios::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>)