Tcl_AddErrorInfo(3)
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NAME
Tcl_AddObjErrorInfo, Tcl_AddErrorInfo, Tcl_SetErrorCode,
Tcl_PosixError - record information about errors
SYNOPSIS
#include <<tcl.h>>
Tcl_AddObjErrorInfo(interp, message, length)
Tcl_AddErrorInfo(interp, message)
Tcl_SetObjErrorCode(interp, errorObjPtr)
Tcl_SetErrorCode(interp, element, element, ... (char *) NULL)
char *
Tcl_PosixError(interp)
ARGUMENTS
Tcl_Interp *interp (in) Interpreter in which to
record information.
char *message (in) For Tcl_AddObjErrorInfo,
this points to the first
byte of an array of
bytes containing a
string to record in the
errorInfo variable.
This byte array may con-
tain embedded null bytes
unless length is nega-
tive. For Tcl_AddError-
Info, this is a conven-
tional C string to
record in the errorInfo
variable.
int length (in) The number of bytes to
copy from message when
setting the errorInfo
variable. If negative,
all bytes up to the
first null byte are
used.
Tcl_Obj *errorObjPtr(in) This variable errorCode
will be set to this
value.
char *element (in) String to record as one
element of errorCode
variable. Last element
argument must be NULL.
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DESCRIPTION
These procedures are used to manipulate two Tcl global
variables that hold information about errors. The vari-
able errorInfo holds a stack trace of the operations that
were in progress when an error occurred, and is intended
to be human-readable. The variable errorCode holds a list
of items that are intended to be machine-readable. The
first item in errorCode identifies the class of error that
occurred (e.g. POSIX means an error occurred in a POSIX
system call) and additional elements in errorCode hold
additional pieces of information that depend on the class.
See the Tcl overview manual entry for details on the vari-
ous formats for errorCode.
The errorInfo variable is gradually built up as an error
unwinds through the nested operations. Each time an error
code is returned to Tcl_EvalObj (or Tcl_Eval, which calls
Tcl_EvalObj) it calls the procedure Tcl_AddObjErrorInfo to
add additional text to errorInfo describing the command
that was being executed when the error occurred. By the
time the error has been passed all the way back to the
application, it will contain a complete trace of the
activity in progress when the error occurred.
It is sometimes useful to add additional information to
errorInfo beyond what can be supplied automatically by
Tcl_EvalObj. Tcl_AddObjErrorInfo may be used for this
purpose: its message and length arguments describe an
additional string to be appended to errorInfo. For exam-
ple, the source command calls Tcl_AddObjErrorInfo to
record the name of the file being processed and the line
number on which the error occurred; for Tcl procedures,
the procedure name and line number within the procedure
are recorded, and so on. The best time to call Tcl_AddOb-
jErrorInfo is just after Tcl_EvalObj has returned
TCL_ERROR. In calling Tcl_AddObjErrorInfo, you may find
it useful to use the errorLine field of the interpreter
(see the Tcl_Interp manual entry for details).
Tcl_AddErrorInfo resembles Tcl_AddObjErrorInfo but differs
in initializing errorInfo from the string value of the
interpreter's result if the error is just starting to be
logged. It does not use the result as a Tcl object so any
embedded null characters in the result will cause informa-
tion to be lost. It also takes a conventional C string in
message instead of Tcl_AddObjErrorInfo's counted string.
The procedure Tcl_SetObjErrorCode is used to set the
errorCode variable. errorObjPtr contains a list object
built up by the caller. errorCode is set to this value.
Tcl_SetObjErrorCode is typically invoked just before
returning an error in an object command. If an error is
returned without calling Tcl_SetObjErrorCode or Tcl_SetEr-
rorCode the Tcl interpreter automatically sets errorCode
to NONE.
The procedure Tcl_SetErrorCode is also used to set the
errorCode variable. However, it takes one or more strings
to record instead of an object. Otherwise, it is similar
to Tcl_SetObjErrorCode in behavior.
Tcl_PosixError sets the errorCode variable after an error
in a POSIX kernel call. It reads the value of the errno C
variable and calls Tcl_SetErrorCode to set errorCode in
the POSIX format. The caller must previously have called
Tcl_SetErrno to set errno; this is necessary on some plat-
forms (e.g. Windows) where Tcl is linked into an applica-
tion as a shared library, or when the error occurs in a
dynamically loaded extension. See the manual entry for
Tcl_SetErrno for more information.
Tcl_PosixError returns a human-readable diagnostic message
for the error (this is the same value that will appear as
the third element in errorCode). It may be convenient to
include this string as part of the error message returned
to the application in the interpreter's result.
It is important to call the procedures described here
rather than setting errorInfo or errorCode directly with
Tcl_ObjSetVar2. The reason for this is that the Tcl
interpreter keeps information about whether these proce-
dures have been called. For example, the first time
Tcl_AddObjErrorInfo is called for an error, it clears the
existing value of errorInfo and adds the error message in
the interpreter's result to the variable before appending
message; in subsequent calls, it just appends the new mes-
sage. When Tcl_SetErrorCode is called, it sets a flag
indicating that errorCode has been set; this allows the
Tcl interpreter to set errorCode to NONE if it receives an
error return when Tcl_SetErrorCode hasn't been called.
If the procedure Tcl_ResetResult is called, it clears all
of the state associated with errorInfo and errorCode (but
it doesn't actually modify the variables). If an error
had occurred, this will clear the error state to make it
appear as if no error had occurred after all.
SEE ALSO
Tcl_DecrRefCount, Tcl_IncrRefCount, Tcl_Interp, Tcl_Rese-
tResult, Tcl_SetErrno
KEYWORDS
error, object, object result, stack, trace, variable