Module: Errno
Relationships & Source Files | |
Defined in: | error.c |
Overview
When an operating system encounters an error, it typically reports the error as an integer error code:
$ ls nosuch.txt
ls: cannot access 'nosuch.txt': No such file or directory
$ echo $? # Code for last error.
2
When the Ruby interpreter interacts with the operating system and receives such an error code (e.g., 2
), it maps the code to a particular Ruby exception class (e.g., Errno::ENOENT
):
File.open('nosuch.txt')
# => No such file or directory @ rb_sysopen - nosuch.txt (Errno::ENOENT)
Each such class is:
-
A nested class in this module,
Errno
. -
A subclass of class
::SystemCallError
. -
Associated with an error code.
Thus:
Errno::ENOENT.superclass # => SystemCallError
Errno::ENOENT::Errno # => 2
The names of nested classes are returned by method Errno.constants
:
Errno.constants.size # => 158
Errno.constants.sort.take(5) # => [:E2BIG, :EACCES, :EADDRINUSE, :EADDRNOTAVAIL, :EADV]
As seen above, the error code associated with each class is available as the value of a constant; the value for a particular class may vary among operating systems. If the class is not needed for the particular operating system, the value is zero:
Errno::ENOENT::Errno # => 2
Errno::ENOTCAPABLE::Errno # => 0
Constant Summary
-
NOERROR =
No error
rb_eNOERROR