Error Handling

IDL contains a system variable that is updated when errors occur. This system variable is described below.

!ERROR_STATE

This system variable is a structure. Whenever an error occurs, IDL sets the fields in this system variable according to the nature of the field. An IDL error is always comprised of an IDL-generated component, and may also contain an operating system-generated component.

NAME - A read-only string variable containing the error name of the IDL-generated component of the last error message. Although the error code-as defined below in CODE-may change between IDL sessions, the name will always remain the same. If an error has not occurred in the current IDL session, this field is set to IDL_M_SUCCESS.

BLOCK - A read-only string variable containing the name of the message block for the IDL-generated component of the last error message. If an error has not occurred in the current IDL session, this field is set to IDL_MBLK_CORE.

CODE - The error code of the IDL-generated component of the last error in IDL. Whenever an error occurs, IDL sets this system variable to the error code (a negative integer number) of the error. Although the error code may change between IDL sessions, the name-as defined above in NAME-will always remain the same. If an error has not occurred in the current IDL session, this field is set to 0.

SYS_CODE - The error code of the operating system-generated component, if it exists, of the last error. IDL sets this system variable to the OS-defined error code.

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 - The error message of the IDL-generated component of the last error. Whenever an error occurs, IDL sets this field to the error message (a scalar string) that corresponds to the error code. If an error has not occurred in the current IDL session, this field is set to the null string, ' '.

SYS_MSG - The error message of the operating system-generated component, if it exists of the last error. When an operating system error occurs, IDL sets this field to the OS-defined error message string. If an error has not occurred in the current IDL session, this field is set to the null string, ' '.

MSG_PREFIX - A string variable containing the prefix string used for the IDL-generated component of error messages.

Using !ERROR_STATE

At the beginning of an IDL session, !ERROR_STATE contains default information. To see this information, you can either view !ERROR_STATE from the System field of the Variable Watch Window (see The Variable Watch Window) or you can enter PRINT, !ERROR_STATE at the Command Input Line. After an error has occurred, all of the fields of !ERROR_STATE display their updated status.

You can use MESSAGE, /RESET_ERROR STATE to reset all the fields in !ERROR_STATE to their default values.