std::iostream_category

C++

Language

Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

Input/output library

I/O manipulators

C-style I/O

Buffers

basic_streambuf

basic_filebuf

basic_stringbuf

strstreambuf (deprecated)

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

istrstream (deprecated)

ostrstream (deprecated)

strstream (deprecated)

Synchronized Output

basic_osyncstream (C++20)

Types

streamoff

streamsize

fpos

Error category interface

iostream_category (C++11)

io_errc (C++11)

Defined in header <ios>
const std::error_category& iostream_category() noexcept;		(since C++11)

Obtains a reference to the static error category object for iostream errors. The object is required to override the virtual function error_category::name() to return a pointer to the string "iostream". It is used to identify error codes provided in the exceptions of type std::ios_base::failure.

Parameters

(none)

Return value

A reference to the static object of unspecified runtime type, derived from std::error_category.

Example

Run this code

#include <iostream>
#include <fstream>

int main()
{
    std::ifstream f("doesn't exist");
    try {
        f.exceptions(f.failbit);
    } catch (const std::ios_base::failure& e) {
        std::cout << "Caught an ios_base::failure.\n"
                  << "Error code: " << e.code().value() 
                  << " (" << e.code().message() << ")\n"
                  << "Error category: " << e.code().category().name() << '\n';

    }
}

Possible output:

Caught an ios_base::failure.
Error code: 1 (unspecified iostream_category error)
Error category: iostream

See also

failure	stream exception (public member class of std::ios_base)
io_errc (C++11)	the IO stream error codes (enum)