< cpp‎ | error
Utilities library
Language support
Type support (basic types, RTTI)
Library feature-test macros (C++20)
Dynamic memory management
Program utilities
Coroutine support (C++20)
Variadic functions
Debugging support
Three-way comparison
General utilities
Date and time
Function objects
Formatting library (C++20)
Relational operators (deprecated in C++20)
Integer comparison functions
Swap and type operations
Common vocabulary types
Elementary string conversions

Diagnostics library
Exception handling
Exception handling failures
(until C++17*)
(until C++17*)
(C++11)(until C++17*)    
(until C++17*)
Error codes
Error codes
Defined in header <system_error>
enum class errc;
(since C++11)

The scoped enumeration std::errc defines the values of portable error conditions that correspond to the POSIX error codes.


[edit] Member constants

Constant Equivalent POSIX Error
address_family_not_supported EAFNOSUPPORT
address_in_use EADDRINUSE
address_not_available EADDRNOTAVAIL
already_connected EISCONN
argument_list_too_long E2BIG
argument_out_of_domain EDOM
bad_address EFAULT
bad_file_descriptor EBADF
bad_message EBADMSG
broken_pipe EPIPE
connection_aborted ECONNABORTED
connection_already_in_progress EALREADY
connection_refused ECONNREFUSED
connection_reset ECONNRESET
cross_device_link EXDEV
destination_address_required EDESTADDRREQ
device_or_resource_busy EBUSY
directory_not_empty ENOTEMPTY
executable_format_error ENOEXEC
file_exists EEXIST
file_too_large EFBIG
filename_too_long ENAMETOOLONG
function_not_supported ENOSYS
host_unreachable EHOSTUNREACH
identifier_removed EIDRM
illegal_byte_sequence EILSEQ
inappropriate_io_control_operation ENOTTY
interrupted EINTR
invalid_argument EINVAL
invalid_seek ESPIPE
io_error EIO
is_a_directory EISDIR
message_size EMSGSIZE
network_down ENETDOWN
network_reset ENETRESET
network_unreachable ENETUNREACH
no_buffer_space ENOBUFS
no_child_process ECHILD
no_link ENOLINK
no_lock_available ENOLCK
no_message_available (deprecated) ENODATA
no_message ENOMSG
no_protocol_option ENOPROTOOPT
no_space_on_device ENOSPC
no_stream_resources (deprecated) ENOSR
no_such_device_or_address ENXIO
no_such_device ENODEV
no_such_file_or_directory ENOENT
no_such_process ESRCH
not_a_directory ENOTDIR
not_a_socket ENOTSOCK
not_a_stream (deprecated) ENOSTR
not_connected ENOTCONN
not_enough_memory ENOMEM
not_supported ENOTSUP
operation_canceled ECANCELED
operation_in_progress EINPROGRESS
operation_not_permitted EPERM
operation_not_supported EOPNOTSUPP
operation_would_block EWOULDBLOCK
owner_dead EOWNERDEAD
permission_denied EACCES
protocol_error EPROTO
protocol_not_supported EPROTONOSUPPORT
read_only_file_system EROFS
resource_deadlock_would_occur EDEADLK
resource_unavailable_try_again EAGAIN
result_out_of_range ERANGE
state_not_recoverable ENOTRECOVERABLE
stream_timeout (deprecated) ETIME
text_file_busy ETXTBSY
timed_out ETIMEDOUT
too_many_files_open_in_system ENFILE
too_many_files_open EMFILE
too_many_links EMLINK
too_many_symbolic_link_levels ELOOP
value_too_large EOVERFLOW
wrong_protocol_type EPROTOTYPE

[edit] Non-member functions

creates error code value for errc enum e
(function) [edit]
creates an error condition for an errc value e
(function) [edit]

[edit] Helper classes

extends the type trait std::is_error_condition_enum to identify errc values as error conditions
(function template) [edit]

[edit] Example

#include <filesystem>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <string>
#include <system_error>
#include <thread>
void print_error(const std::string& details, std::error_code error_code)
    std::string value_name;
    if (error_code == std::errc::invalid_argument)
        value_name = "std::errc::invalid_argument";
    if (error_code == std::errc::no_such_file_or_directory)
        value_name = "std::errc::no_such_file_or_directory";
    if (error_code == std::errc::is_a_directory)
        value_name = "std::errc::is_a_directory";
    if (error_code == std::errc::permission_denied)
        value_name = "std::errc::permission_denied";
    std::cout << details << ":\n  "
              << std::quoted(error_code.message())
              << " (" << value_name << ")\n\n";
void print_errno(const std::string& details, int errno_value = errno)
    print_error(details, std::make_error_code(std::errc(errno_value)));
int main()
    std::cout << "Detaching a not-a-thread...\n";
    catch (const std::system_error& e)
        print_error("Error detaching empty thread", e.code());
    std::cout << "Opening nonexistent file...\n";
    std::ifstream nofile{"nonexistent-file"};
    if (!nofile.is_open())
        print_errno("Error opening nonexistent file for reading");
    std::cout << "Reading from directory as a file...\n";
    std::ifstream dir_stream{"dir"};
    [[maybe_unused]] char c = dir_stream.get();
    if (!dir_stream.good())
        print_errno("Error reading data from directory");
    std::cout << "Open read-only file for writing...\n";
    std::fstream{"readonly-file", std::ios::out};
    std::filesystem::permissions("readonly-file", std::filesystem::perms::owner_read);
    std::fstream write_readonly("readonly-file", std::ios::out);
    if (!write_readonly.is_open())
        print_errno("Error opening read-only file for writing");

Possible output:

Detaching a not-a-thread...
Error detaching empty thread:
  "Invalid argument" (std::errc::invalid_argument)
Opening nonexistent file...
Error opening nonexistent file for reading:
  "No such file or directory" (std::errc::no_such_file_or_directory)
Reading from directory as a file...
Error reading data from directory:
  "Is a directory" (std::errc::is_a_directory)
Open read-only file for writing...
Error opening read-only file for writing:
  "Permission denied" (std::errc::permission_denied)

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 3869 C++11 the member constants no_message_available,
no_stream_resources, not_a_stream and stream_timeout
referred to the obsolete POSIX STREAMS API[1]
deprecated them
  1. Although the corresponding POSIX error numbers ENODATA, ENOSR, ENOSTR and ETIME were marked "obsolescent" in POSIX 2017, the STREAMS API was optional and not required for conformance to the previous POSIX standard (because popular unix-like systems refused to implement it).

[edit] See also

holds a platform-dependent error code
(class) [edit]
holds a portable error code
(class) [edit]