Ruby Study 10 : Exception Handling

Ruby exception objects are subclasses of Exception. However, operating systems typically report errors using plain integers. Module Errno is created dynamically to map these operating system errors to Ruby classes, with each error number generating its own subclass of SystemCallError. As the subclass is created in module Errno, its name will start Errno::.

The names of the Errno:: classes depend on the environment in which Ruby runs. On a typical Unix or Windows platform, there are Errno classes such as Errno::EACCES, Errno::EAGAIN, Errno::EINTR, and so on.

The integer operating system error number corresponding to a particular error is available as the class constantErrno::error::Errno.

   Errno::EACCES::Errno   #=> 13    Errno::EAGAIN::Errno   #=> 11    Errno::EINTR::Errno    #=> 4 

The full list of operating system errors on your particular platform are available as the constants of Errno.

   Errno.constants   #=> :E2BIG, :EACCES, :EADDRINUSE, :EADDRNOTAVAIL, ...

p Errno.constants.sort
[:E2BIG, :EACCES, :EADDRINUSE, :EADDRNOTAVAIL, :EADV, :EAFNOSUPPORT, :EAGAIN, :EALREADY, :EAUTH, :EBADE, :EBADF, :EBADFD, :EBADMSG, :EBADR, :EBADRPC, :EBADRQC, :EBADSLT, :EBFONT, :EBUSY, :ECANCELED, :ECHILD, :ECHRNG, :ECOMM, :ECONNABORTED, :ECONNREFUSED, :ECONNRESET, :EDEADLK, :EDEADLOCK, :EDESTADDRREQ, :EDOM, :EDOOFUS, :EDOTDOT, :EDQUOT, :EEXIST, :EFAULT, :EFBIG, :EFTYPE, :EHOSTDOWN, :EHOSTUNREACH, :EIDRM, :EILSEQ, :EINPROGRESS, :EINTR, :EINVAL, :EIO, :EIPSEC, :EISCONN, :EISDIR, :EISNAM, :EKEYEXPIRED, :EKEYREJECTED, :EKEYREVOKED, :EL2HLT, :EL2NSYNC, :EL3HLT, :EL3RST, :ELIBACC, :ELIBBAD, :ELIBEXEC, :ELIBMAX, :ELIBSCN, :ELNRNG, :ELOOP, :EMEDIUMTYPE, :EMFILE, :EMLINK, :EMSGSIZE, :EMULTIHOP, :ENAMETOOLONG, :ENAVAIL, :ENEEDAUTH, :ENETDOWN, :ENETRESET, :ENETUNREACH, :ENFILE, :ENOANO, :ENOATTR, :ENOBUFS, :ENOCSI, :ENODATA, :ENODEV, :ENOENT, :ENOEXEC, :ENOKEY, :ENOLCK, :ENOLINK, :ENOMEDIUM, :ENOMEM, :ENOMSG, :ENONET, :ENOPKG, :ENOPROTOOPT, :ENOSPC, :ENOSR, :ENOSTR, :ENOSYS, :ENOTBLK, :ENOTCONN, :ENOTDIR, :ENOTEMPTY, :ENOTNAM, :ENOTRECOVERABLE, :ENOTSOCK, :ENOTSUP, :ENOTTY, :ENOTUNIQ, :ENXIO, :EOPNOTSUPP, :EOVERFLOW, :EOWNERDEAD, :EPERM, :EPFNOSUPPORT, :EPIPE, :EPROCLIM, :EPROCUNAVAIL, :EPROGMISMATCH, :EPROGUNAVAIL, :EPROTO, :EPROTONOSUPPORT, :EPROTOTYPE, :ERANGE, :EREMCHG, :EREMOTE, :EREMOTEIO, :ERESTART, :ERFKILL, :EROFS, :ERPCMISMATCH, :ESHUTDOWN, :ESOCKTNOSUPPORT, :ESPIPE, :ESRCH, :ESRMNT, :ESTALE, :ESTRPIPE, :ETIME, :ETIMEDOUT, :ETOOMANYREFS, :ETXTBSY, :EUCLEAN, :EUNATCH, :EUSERS, :EWOULDBLOCK, :EXDEV, :EXFULL, :NOERROR]

for err in Errno.constants.sort do 
   errnum = eval( "Errno::#{err}::Errno" )
   print( "#{err} #{errnum} ," ) 
end
结果
E2BIG 7 ,EACCES 13 ,EADDRINUSE 10048 ,EADDRNOTAVAIL 10049 ,EADV 0 ,EAFNOSUPPORT 10047 ,EAGAIN 11 ,EALREADY 10037 ,EAUTH 0 ,EBADE 0 ,EBADF 9 ,EBADFD 0 ,EBADMSG 0 ,EBADR 0 ,EBADRPC 0 ,EBADRQC 0 ,EBADSLT 0 ,EBFONT 0 ,EBUSY 16 ,ECANCELED 0 ,ECHILD 10 ,ECHRNG 0 ,ECOMM 0 ,ECONNABORTED 10053 ,ECONNREFUSED 10061 ,ECONNRESET 10054 ,EDEADLK 36 ,EDEADLOCK 36 ,EDESTADDRREQ 10039 ,EDOM 33 ,EDOOFUS 0 ,EDOTDOT 0 ,EDQUOT 10069 ,EEXIST 17 ,EFAULT 14 ,EFBIG 27 ,EFTYPE 0 ,EHOSTDOWN 10064 ,EHOSTUNREACH 10065 ,EIDRM 0 ,EILSEQ 42 ,EINPROGRESS 10036 ,EINTR 4 ,EINVAL 22 ,EIO 5 ,EIPSEC 0 ,EISCONN 10056 ,EISDIR 21 ,EISNAM 0 ,EKEYEXPIRED 0 ,EKEYREJECTED 0 ,EKEYREVOKED 0 ,EL2HLT 0 ,EL2NSYNC 0 ,EL3HLT 0 ,EL3RST 0 ,ELIBACC 0 ,ELIBBAD 0 ,ELIBEXEC 0 ,ELIBMAX 0 ,ELIBSCN 0 ,ELNRNG 0 ,ELOOP 10062 ,EMEDIUMTYPE 0 ,EMFILE 24 ,EMLINK 31 ,EMSGSIZE 10040 ,EMULTIHOP 0 ,ENAMETOOLONG 38 ,ENAVAIL 0 ,ENEEDAUTH 0 ,ENETDOWN 10050 ,ENETRESET 10052 ,ENETUNREACH 10051 ,ENFILE 23 ,ENOANO 0 ,ENOATTR 0 ,ENOBUFS 10055 ,ENOCSI 0 ,ENODATA 0 ,ENODEV 19 ,ENOENT 2 ,ENOEXEC 8 ,ENOKEY 0 ,ENOLCK 39 ,ENOLINK 0 ,ENOMEDIUM 0 ,ENOMEM 12 ,ENOMSG 0 ,ENONET 0 ,ENOPKG 0 ,ENOPROTOOPT 10042 ,ENOSPC 28 ,ENOSR 0 ,ENOSTR 0 ,ENOSYS 40 ,ENOTBLK 0 ,ENOTCONN 10057 ,ENOTDIR 20 ,ENOTEMPTY 41 ,ENOTNAM 0 ,ENOTRECOVERABLE 0 ,ENOTSOCK 10038 ,ENOTSUP 0 ,ENOTTY 25 ,ENOTUNIQ 0 ,ENXIO 6 ,EOPNOTSUPP 10045 ,EOVERFLOW 0 ,EOWNERDEAD 0 ,EPERM 1 ,EPFNOSUPPORT 10046 ,EPIPE 32 ,EPROCLIM 10067 ,EPROCUNAVAIL 0 ,EPROGMISMATCH 0 ,EPROGUNAVAIL 0 ,EPROTO 0 ,EPROTONOSUPPORT 10043 ,EPROTOTYPE 10041 ,ERANGE 34 ,EREMCHG 0 ,EREMOTE 10071 ,EREMOTEIO 0 ,ERESTART 0 ,ERFKILL 0 ,EROFS 30 ,ERPCMISMATCH 0 ,ESHUTDOWN 10058 ,ESOCKTNOSUPPORT 10044 ,ESPIPE 29 ,ESRCH 3 ,ESRMNT 0 ,ESTALE 10070 ,ESTRPIPE 0 ,ETIME 0 ,ETIMEDOUT 10060 ,ETOOMANYREFS 10059 ,ETXTBSY 0 ,EUCLEAN 0 ,EUNATCH 0 ,EUSERS 10068 ,EWOULDBLOCK 10035 ,EXDEV 18 ,EXFULL 0 ,NOERROR 0 ,

#!/opt/ruby/bin/ruby
def doCalc
    begin
        print( "Enter a number: " )
        aNum = gets().chomp()
        result = 100 / aNum.to_i
    rescue Exception => e
        result = 0
        puts( "Error: " + e.to_s + "\nPlease try again." )    # Ruby 1.9如果要在字符连接中使用Exception的返回值, 需要使用to_s方法.
        retry           # retry on exception
    else
        msg = "Result = #{result}"
    ensure
        msg = "You entered '#{aNum}'. " + msg
    end
    return msg
end
doCalc

./test.rb 
Enter a number: 0
Error: divided by 0
Please try again.
Enter a number: "1"
Error: divided by 0
Please try again.
Enter a number: a
Error: divided by 0
Please try again.
Enter a number: 10

#!/opt/ruby/bin/ruby
def doCalc
    tries = 0
    begin
        tries += 1
        print( "Enter a number: " )
        aNum = gets().chomp()
        result = 100 / aNum.to_i   
    rescue Exception => e      
        msg = "Error: " + e.to_s
        puts( msg )
        puts( "tries = #{tries}" )
        result = 0      
        if tries < 3 then # set a fixed number of retries
           retry 
        end         
    else
        msg = "Result = #{result}"
    ensure
        msg = "You entered '#{aNum}'. " + msg
    end
    return msg
end
doCalc

./test.rb 
Enter a number: a
Error: divided by 0
tries = 1
Enter a number: b
Error: divided by 0
tries = 2
Enter a number: c
Error: divided by 0
tries = 3

   raise "Failed to create socket"    raise ArgumentError, "No parameters", caller

begin
    raise ZeroDivisionError.new( "I'm afraid you divided by Zero" )
rescue Exception => e
    puts( e.class )
    puts( "message: " + e.to_s )
end

ZeroDivisionError
message: I'm afraid you divided by Zero

class NoNameError < Exception
    def to_str
        "No Name given!"
    end
end
def sayHello( aName )
    begin
        if (aName == "") or (aName == nil) then
             raise NoNameError 
        end
    rescue Exception => e
        puts( e.class )
        puts( "error message: " + e.to_s )
        puts( e.backtrace )
    else
        puts( "Hello #{aName}" )
    end
end
sayHello(nil)

NoNameError
error message: NoNameError
C:/Users/digoal/Desktop/new.rb:9:in `sayHello'
C:/Users/digoal/Desktop/new.rb:19:in `<main>'

   def a      raise "boom"    end     def b      a()    end     begin      b()    rescue => detail      print detail.backtrace.join("\n")    end

  prog.rb:2:in `a'    prog.rb:6:in `b'    prog.rb:10

def calc
        result = 1/0
    rescue Exception => e
        puts( e.class )
        puts( e )
        result = nil
    return result
end

class X
        @@x = 1/0
    rescue Exception => e
        puts( e.class )
        puts( e )
end

module Y
        @@x = 1/0
    rescue Exception => e
        puts( e.class )
        puts( e )
end