After an error has occurred, this variable will be set to hold
additional information about the error in a form that is easy
to process with programs.
errorCode consists of a Tcl list with one or more elements.
The first element of the list identifies a general class of
errors, and determines the format of the rest of the list.
The following formats for errorCode are used by the
Tcl core; individual applications may define additional formats.
- ARITH code msg
-
This format is used when an arithmetic error occurs (e.g. an attempt
to divide by zero in the expr command).
Code identifies the precise error and msg provides a
human-readable description of the error. Code will be either
DIVZERO (for an attempt to divide by zero),
DOMAIN (if an argument is outside the domain of a function, such as acos(-3)),
IOVERFLOW (for integer overflow),
OVERFLOW (for a floating-point overflow),
or UNKNOWN (if the cause of the error cannot be determined).
- CHILDKILLED pid sigName msg
-
This format is used when a child process has been killed because of
a signal. The second element of errorCode will be the
process's identifier (in decimal).
The third element will be the symbolic name of the signal that caused
the process to terminate; it will be one of the names from the
include file signal.h, such as SIGPIPE.
The fourth element will be a short human-readable message
describing the signal, such as ``write on pipe with no readers''
for SIGPIPE.
- CHILDSTATUS pid code
-
This format is used when a child process has exited with a non-zero
exit status. The second element of errorCode will be the
process's identifier (in decimal) and the third element will be the exit
code returned by the process (also in decimal).
- CHILDSUSP pid sigName msg
-
This format is used when a child process has been suspended because
of a signal.
The second element of errorCode will be the process's identifier,
in decimal.
The third element will be the symbolic name of the signal that caused
the process to suspend; this will be one of the names from the
include file signal.h, such as SIGTTIN.
The fourth element will be a short human-readable message
describing the signal, such as ``background tty read''
for SIGTTIN.
- NONE
-
This format is used for errors where no additional information is
available for an error besides the message returned with the
error. In these cases errorCode will consist of a list
containing a single element whose contents are NONE.
- POSIX errName msg
-
If the first element of errorCode is POSIX, then
the error occurred during a POSIX kernel call.
The second element of the list will contain the symbolic name
of the error that occurred, such as ENOENT; this will
be one of the values defined in the include file errno.h.
The third element of the list will be a human-readable
message corresponding to errName, such as
``no such file or directory'' for the ENOENT case.
To set errorCode, applications should use library
procedures such as Tcl_SetErrorCode and Tcl_PosixError,
or they may invoke the error command.
If one of these methods hasn't been used, then the Tcl
interpreter will reset the variable to NONE after
the next error.