std::ios_base::openmode - cppreference.com

From cppreference.com

`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

#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:

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

Example

See also