Commands: try/catch

Syntax

try { <level> } "{"
   <commands>
"}"

catch <exception> "{"
   <commands>
"}"

Description

try:   Execute a command block which detects exceptions.
catch: Catch an exception detected within the corresponding try command block.

Parameters

• <level>
  A numeric value indicating which severity level of exceptions are to be detected. If during execution of the command block an exception is thrown with a severity level greater than <level> it is ignored. If this parameter is omitted, then the value of throw_level is assumed, or 6 if throw_level has not been set.

• <exception>
  An exception identifier with details of the caught exception. If this identifier does not exist a local exception is created.

• <commands>
  A series of language commands to be executed within the try or catch block.

Switches

none

Notes

Two types of exception can be thrown within a try block: system exceptions and user exceptions:

System exceptions are thrown as a result of language or data errors detected by the system. This is done automatically without any user action.

User exceptions are thrown by a throw command, typically executed as a result of an error detected by application macro code.

Exceptions detected within a try command block may be thrown in the current command frame or in sub-frames, e.g. called functions or procedures.

Examples

Code to catch a maths warning:

try 10 {
   numeric x = sqrt(-10);# A mathematical anomaly
# We will never get here
}
catch exc {
# Just list the error details
    list exc
}

See Also