egghelp/eggheads community

problem with the catch command

2003-04-09T12:42:12-04:00

hehe ok
I agree with u

Statistics: Posted by Guest — Wed Apr 09, 2003 12:42 pm

problem with the catch command

2003-04-09T11:56:21-04:00

OOPs, no, not directed at you.

Though the first sentance did apply. It aint allways easy to learn a new language, when you are used to antoher.

Statistics: Posted by ppslim — Wed Apr 09, 2003 11:56 am

problem with the catch command

2003-04-09T11:22:44-04:00

There are many however, that tend to thing "It doens't work the way X language works, it is crap".

The worst people are the ones that put another laguage down, for not doing what they want, when it is often them forgetting that method are not the same.

Is this referring to me?
I only said im used to java

Statistics: Posted by Guest — Wed Apr 09, 2003 11:22 am

problem with the catch command

2003-04-09T11:10:55-04:00

There are many people various programming backgrounds. Switch to and from a new language isn't allways easy.

There are many however, that tend to thing "It doens't work the way X language works, it is crap".

The worst people are the ones that put another laguage down, for not doing what they want, when it is often them forgetting that method are not the same.

Statistics: Posted by ppslim — Wed Apr 09, 2003 11:10 am

problem with the catch command

2003-04-09T10:46:10-04:00

ok thanks again

/me is Java programmer .. works abit different there

Statistics: Posted by Guest — Wed Apr 09, 2003 10:46 am

problem with the catch command

2003-04-09T10:32:22-04:00

The return value is detmined by the last command to take place.

Each and every command returns a value. In many cases, thsi value is invisible to normal Tcl. Take the following examples, and I will show you what they return.

Code:

proc hand {} {  return 1}proc test1 {} {  set a [hand]  return $a}proc test2 {} {  return [hand]}proc test3 {} {  hand}

Test1, 2 & 3 all return 1

Test1 is obvious to how it works, and test2 is a simplified version.

In test3, the command "hand" is called. The return value (no the return code) is set to 1. Once it comes back down into test3, the return value buffer is not cleared (the return value buffer is cleared at the start of calling a command). Because there is still a value in the buffer, it is also returned by test3.

The "set" command, returns that value of the variable passed, or the value it has just been set to. In other words, the reason what your catch stament is called.

In your first catch block, you have the "close" command. This doesn't return any value at all. As noted above, the buffer is cleared at the start of a command, and because it isn't filled again by the close command, there is nothing in the rturn value.

The way to your script working, is not to test the value of the err_msg variable. It is to test the value returned from the catch command. It returns 1 on error, 0 on all ok (TCL_OK).

EG

Code:

proc create_file_from_list {filename data_list} {   if {[catch {     set fc [open $filename w]     puts -nonewline $fc $data_list     close $fc   } err_msg]} {    return [list -1 "Error while writing file"]   } else {     return [list 0]   } }

Statistics: Posted by ppslim — Wed Apr 09, 2003 10:32 am

problem with the catch command

2003-04-09T10:22:20-04:00

Ok now it's clear to me
Thanks for your time.

Statistics: Posted by Guest — Wed Apr 09, 2003 10:22 am

problem with the catch command

2003-04-09T10:23:28-04:00

My point is : How is the return-value from 'script' determined?

It returns the value of the last executed command before leaving the proc.

Example:

Code:

catch {    set value 1    set value 2} err_msg puts "The Error Message:"puts $err_msg

Assuming your script has no errors, the last successfully executed command is the [close $fc].

http://www.tcl.tk/man/tcl8.4/TclCmd/close.htm says:

The command returns an empty string, and may generate an error if an error occurs while flushing output.

What you should test for, is the value the [catch] command returns, not the err_msg.

Statistics: Posted by egghead — Wed Apr 09, 2003 10:14 am

problem with the catch command

2003-04-09T09:56:29-04:00

Yes , I read that.
But why doesnt err_msg get set in the first code-sample? Cause this code also contains a 'set' line?

Code:

set fc [open $filename w]

Does err_msg only get set to the return value when there's only one command between the catch-braces ? (Or when its the last line maybe?)

My point is : How is the return-value from 'script' determined?

Statistics: Posted by Guest — Wed Apr 09, 2003 9:56 am

Re: problem with the catch command

2003-04-09T09:41:45-04:00

Now the following code seems to set the error_msg var ALWAYS, even when the datetime_string is in the correct format.

Can someone tell me why?
Thanks.

http://www.tcl.tk/man/tcl8.4/TclCmd/catch.htm says:

If script does not raise an error, catch will return 0 (TCL_OK) and set the variable to the value returned from script.

Statistics: Posted by egghead — Wed Apr 09, 2003 9:41 am

problem with the catch command

2003-04-09T09:14:10-04:00

Hi ppl,

Hope someone can help me out with this.

This code returns a list containing an errormsg when there occured a problem while writing the file, no errormsg if the writing was succesful:

Code:

proc create_file_from_list {filename data_list} {   catch {    set fc [open $filename w]    puts -nonewline $fc $data_list    close $fc  } err_msg  if {$err_msg!=""} {    return [list -1 "Error while writing file"]  } else {    return [list 0]  }}

Now the following code seems to set the error_msg var ALWAYS, even when the datetime_string is in the correct format.

Code:

catch {    set timestamp [clock scan $datetime_string]  } err_msg  if {$err_msg!=""} {    return [list -1 "Invalid format for 'date'. Correct format: $timestamp_format"]  } else {    return [list 0 $timestamp]  }

Can someone tell me why?
Thanks.

Statistics: Posted by Guest — Wed Apr 09, 2003 9:14 am