Error Handling System Variables

The following system variables are either set by IDL when an error condition occurs or used by IDL when displaying information about errors.

!ERR

This system variable is now obsolete and has been replaced by the !ERROR_STATE system variable. Code that uses the !ERR system variable will continue to function as before, but all new code should use !ERROR_STATE.CODE.

!ERROR_STATE

A structure variable which contains the status of the last error message. !ERROR_STATE includes the following fields:

NAME: A read-only string variable containing the error name of the IDL-generated component of the last error message.

BLOCK: A read-only string variable containing the name of the message block for the last error message's IDL-generated component.

Note

External Development Guide

CODE: A long-integer variable containing the error code of the last error's IDL-generated component.

SYS_CODE: A long-integer variable containing the error code of the last error's operating system-generated component, if it exists.

For historical reasons, SYS_CODE is a two-element longword array. The first element of the array (that is, SYS_CODE[0]) contains the OS-defined error code. The second element of the array is not used, and always contains zero. Either !ERROR_STATE.SYS_CODE or !ERROR_STATE.SYS_CODE[0] will return the relevant error code.

SYS_CODE_TYPE: A string describing the type of system code contained in SYS_CODE. A null string in this field indicates that there is no system code corresponding to the current error. The possible non-NULL values are:


Value	Meaning
errno	Unix/Posix system error
win32	Microsoft Windows Win32 system error
winsock	Microsoft Windows sockets library error

MSG: A read-only string variable containing the text of the last IDL-generated error message.

SYS_MSG: A read-only string variable containing the text of the last error's operating system-generated component, if it exists.

MSG_PREFIX: A string variable containing the prefix string used for error messages.

This system variable replaces !ERROR, !ERR_STRING, !MSG_PREFIX, !SYSERR_STRING, and !SYSERROR, and includes two new fields: error name and block name. For a more detailed explanation of !ERROR_STATE, see Error Handling.

!ERROR

This system variable is now obsolete and has been replaced by the !ERROR_STATE system variable. Code that uses the !ERROR system variable will continue to function as before, but we suggest that all new code use !ERROR_STATE.CODE.

!ERR_STRING

This system variable is now obsolete and has been replaced by the !ERROR_STATE system variable. Code that uses the !ERR_STRING system variable will continue to function as before, but we suggest that all new code use !ERROR_STATE.MSG.

!EXCEPT

An integer variable that controls when IDL checks for invalid mathematical computations (exceptions), such as division by zero. The three allowed values are:

Value	Description
0	Never report exceptions.
1	Report exceptions when the interpreter is returning to an interactive prompt (the default).
2	Report exceptions at the end of each IDL statement. Note that this slows IDL by roughly 5% compared to setting !EXCEPT=1.

For more information on invalid mathematical computations and error reporting, see Math Errors.

The value of !EXCEPT is used by the CHECK_MATH function to determine when to return errors. See CHECK_MATH for details.

!MOUSE

A structure variable that contains the status from the last cursor read operation. !MOUSE has the following fields:

X and Y: Contain the location (in device coordinates) of the cursor when the mouse button was pressed.

BUTTON: Contains

1 (one) if the left mouse button was pressed,

2 (two) if the middle mouse button was pressed

4 (four) if the right mouse button was pressed.

TIME: Contains the number of milliseconds since a base time.

!MSG_PREFIX

This keyword is now obsolete and has been replaced by the !ERROR_STATE system variable. Code that uses the !MSG_PREFIX system variable will continue to function as before, but we suggest that all new code use !ERROR_STATE.MSG_PREFIX.

!SYSERROR

This keyword is now obsolete and has been replaced by the !ERROR_STATE system variable. Code that uses the !SYSERROR system variable will continue to function as before, but we suggest that all new code use !ERROR_STATE.SYS_CODE.

!SYSERR_STRING

This keyword is now obsolete and has been replaced by the !ERROR_STATE system variable. Code that uses the !SYSERR_STRING system variable will continue to function as before, but we suggest that all new code use !ERROR_S class="cItalic">TATE.SYS_MSG.

!WARN

A structure variable that causes IDL to print warnings to the console or command log when obsolete IDL features are found at compile time. !WARN has the following fields:

Setting each of the three fields to 1 (one) generates a warning for a different type of obsolete code. If the OBS_ROUTINES field is set equal to one, IDL generates warnings when it encounters references to obsolete internal or library routines. If the OBS_SYSVARS field is set equal to one, IDL generates warnings when it encounters references to obsolete system variables. If the PARENS field is set equal to one, IDL generates warnings when it encounters a use of parentheses to specify an index into an array. No warnings are generated when the fields of the !WARN structure are set equal to zero (the default).