Tcl_AddErrorInfo(3) Tcl Library Procedures Tcl_AddErrorInfo(3) ______________________________________________________________________________
NAME
Tcl_GetReturnOptions, Tcl_SetReturnOptions, Tcl_AddErrorInfo,
Tcl_AppendObjToErrorInfo, Tcl_AddObjErrorInfo, Tcl_SetObjErrorCode,
Tcl_SetErrorCode, Tcl_SetErrorCodeVA, Tcl_SetErrorLine,
Tcl_GetErrorLine, Tcl_PosixError, Tcl_LogCommandInfo - retrieve or
record information about errors and other return options
SYNOPSIS
#include <tcl.h>
Tcl_Obj *
Tcl_GetReturnOptions(interp, code)
int
Tcl_SetReturnOptions(interp, options)
Tcl_AddErrorInfo(interp, message)
Tcl_AppendObjToErrorInfo(interp, objPtr)
Tcl_AddObjErrorInfo(interp, message, length)
Tcl_SetObjErrorCode(interp, errorObjPtr)
Tcl_SetErrorCode(interp, element, element, ... (char *)NULL)
Tcl_SetErrorCodeVA(interp, argList)
Tcl_GetErrorLine(interp)
Tcl_SetErrorLine(interp, lineNum)
const char *
Tcl_PosixError(interp)
void
Tcl_LogCommandInfo(interp, script, command, commandLength)
ARGUMENTS
Tcl_Interp *interp (in) Interpreter in which to record
information.
int code The code returned from script evaluation.
Tcl_Obj *options A dictionary of return options.
const char *message (in) For Tcl_AddErrorInfo, this is a
conventional C string to append
to the -errorinfo return option.
For Tcl_AddObjErrorInfo, this
points to the first byte of an
array of length bytes containing
a string to append to the
-errorinfo return option. This
byte array may contain embedded
null bytes unless length is
negative.
Tcl_Obj *objPtr (in) A message to be appended to the
-errorinfo return option in the
form of a Tcl_Obj value.
int length (in) The number of bytes to copy from
message when appending to the
-errorinfo return option. If
negative, all bytes up to the
first null byte are used.
Tcl_Obj *errorObjPtr (in) The -errorcode return option
will be set to this value.
const char *element (in) String to record as one element
of the -errorcode return option.
Last element argument must be
(char *)NULL.
va_list argList (in) An argument list which must have
been initialized using va_start,
and cleared using va_end.
int lineNum The line number of a script where an error
occurred.
const char *script (in) Pointer to first character in
script containing command (must
be <= command)
const char *command (in) Pointer to first character in
command that generated the error
int commandLength (in) Number of bytes in command; -1
means use all bytes up to first
null byte
______________________________________________________________________________
DESCRIPTION
The Tcl_SetReturnOptions and Tcl_GetReturnOptions routines expose the
same capabilities as the return and catch commands, respectively, in
the form of a C interface.
Tcl_GetReturnOptions retrieves the dictionary of return options from an
interpreter following a script evaluation. Routines such as Tcl_Eval
are called to evaluate a script in an interpreter. These routines
return an integer completion code. These routines also leave in the
interpreter both a result and a dictionary of return options generated
by script evaluation. Just as Tcl_GetObjResult retrieves the result,
Tcl_GetReturnOptions retrieves the dictionary of return options. The
integer completion code should be passed as the code argument to
Tcl_GetReturnOptions so that all required options will be present in
the dictionary. Specifically, a code value of TCL_ERROR will ensure
that entries for the keys -errorinfo, -errorcode, and -errorline will
appear in the dictionary. Also, the entries for the keys -code and
-level will be adjusted if necessary to agree with the value of code.
The (Tcl_Obj *) returned by Tcl_GetReturnOptions points to an unshared
Tcl_Obj with reference count of zero. The dictionary may be written
to, either adding, removing, or overwriting any entries in it, without
the need to check for a shared value. As with any Tcl_Obj with
reference count of zero, it is up to the caller to arrange for its
disposal with Tcl_DecrRefCount or to a reference to it via
Tcl_IncrRefCount (or one of the many functions that call that, notably
including Tcl_SetObjResult and Tcl_SetVar2Ex).
A typical usage for Tcl_GetReturnOptions is to retrieve the stack trace
when script evaluation returns TCL_ERROR, like so:
int code = Tcl_Eval(interp, script);
if (code == TCL_ERROR) {
Tcl_Obj *options = Tcl_GetReturnOptions(interp, code);
Tcl_Obj *key = Tcl_NewStringObj("-errorinfo", -1);
Tcl_Obj *stackTrace;
Tcl_IncrRefCount(key);
Tcl_DictObjGet(NULL, options, key, &stackTrace);
Tcl_DecrRefCount(key);
/* Do something with stackTrace */
Tcl_DecrRefCount(options);
}
Tcl_SetReturnOptions sets the return options of interp to be options.
If options contains any invalid value for any key, TCL_ERROR will be
returned, and the interp result will be set to an appropriate error
message. Otherwise, a completion code in agreement with the -code and
-level keys in options will be returned.
As an example, Tcl's return command itself could be implemented in
terms of Tcl_SetReturnOptions like so:
if ((objc % 2) == 0) { /* explicit result argument */
objc--;
Tcl_SetObjResult(interp, objv[objc]);
}
return Tcl_SetReturnOptions(interp, Tcl_NewListObj(objc-1, objv+1));
(It is not really implemented that way. Internal access privileges
allow for a more efficient alternative that meshes better with the
bytecode compiler.)
Note that a newly created Tcl_Obj may be passed in as the options
argument without the need to tend to any reference counting. This is
analogous to Tcl_SetObjResult.
While Tcl_SetReturnOptions provides a general interface to set any
collection of return options, there are a handful of return options
that are very frequently used. Most notably the -errorinfo and
-errorcode return options should be set properly when the command
procedure of a command returns TCL_ERROR. The -errorline return option
is also read by commands that evaluate scripts and wish to supply
detailed error location information in the stack trace text they append
to the -errorinfo option. Tcl provides several simpler interfaces to
more directly set these return options.
The -errorinfo option holds a stack trace of the operations that were
in progress when an error occurred, and is intended to be human-
readable. The -errorcode option holds a Tcl list of items that are
intended to be machine-readable. The first item in the -errorcode
value identifies the class of error that occurred (e.g., POSIX means an
error occurred in a POSIX system call) and additional elements hold
additional pieces of information that depend on the class. See the
manual entry on the errorCode variable for details on the various
formats for the -errorcode option used by Tcl's built-in commands.
The -errorinfo option value is gradually built up as an error unwinds
through the nested operations. Each time an error code is returned to
Tcl_Eval, or any of the routines that performs script evaluation, the
procedure Tcl_AddErrorInfo is called to add additional text to the
-errorinfo value 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 the -errorinfo
value beyond what can be supplied automatically by the script
evaluation routines. Tcl_AddErrorInfo may be used for this purpose:
its message argument is an additional string to be appended to the
-errorinfo option. For example, when an error arises during the source
command, the procedure Tcl_AddErrorInfo is called to record the name of
the file being processed and the line number on which the error
occurred. Likewise, when an error arises during evaluation of a Tcl
procedures, the procedure name and line number within the procedure are
recorded, and so on. The best time to call Tcl_AddErrorInfo is just
after a script evaluation routine has returned TCL_ERROR. The value of
the -errorline return option (retrieved via a call to
Tcl_GetReturnOptions) often makes up a useful part of the message
passed to Tcl_AddErrorInfo.
Tcl_AppendObjToErrorInfo is an alternative interface to the same
functionality as Tcl_AddErrorInfo. Tcl_AppendObjToErrorInfo is called
when the string value to be appended to the -errorinfo option is
available as a Tcl_Obj instead of as a char array.
Tcl_AddObjErrorInfo is nearly identical to Tcl_AddErrorInfo, except
that it has an additional length argument. This allows the message
string to contain embedded null bytes. This is essentially never a
good idea. If the message needs to contain the null character U+0000,
Tcl's usual internal encoding rules should be used to avoid the need
for a null byte. If the Tcl_AddObjErrorInfo interface is used at all,
it should be with a negative length value.
The procedure Tcl_SetObjErrorCode is used to set the -errorcode return
option to the list value errorObjPtr built up by the caller.
Tcl_SetObjErrorCode is typically invoked just before returning an
error. If an error is returned without calling Tcl_SetObjErrorCode or
Tcl_SetErrorCode the Tcl interpreter automatically sets the -errorcode
return option to NONE.
The procedure Tcl_SetErrorCode is also used to set the -errorcode
return option. However, it takes one or more strings to record instead
of a value. Otherwise, it is similar to Tcl_SetObjErrorCode in
behavior.
Tcl_SetErrorCodeVA is the same as Tcl_SetErrorCode except that instead
of taking a variable number of arguments it takes an argument list.
The procedure Tcl_GetErrorLine is used to read the integer value of the
-errorline return option without the overhead of a full call to
Tcl_GetReturnOptions. Likewise, Tcl_SetErrorLine sets the -errorline
return option value.
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 the -errorcode return option in the POSIX
format. The caller must previously have called Tcl_SetErrno to set
errno; this is necessary on some platforms (e.g. Windows) where Tcl is
linked into an application 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
the -errorcode value). It may be convenient to include this string as
part of the error message returned to the application in the
interpreter's result.
Tcl_LogCommandInfo is invoked after an error occurs in an interpreter.
It adds information about the command that was being executed when the
error occurred to the -errorinfo value, and the line number stored
internally in the interpreter is set.
In older releases of Tcl, there was no Tcl_GetReturnOptions routine.
In its place, the global Tcl variables errorInfo and errorCode were the
only place to retrieve the error information. Much existing code
written for older Tcl releases still access this information via those
global variables.
It is important to realize that while reading from those global
variables remains a supported way to access these return option values,
it is important not to assume that writing to those global variables
will properly set the corresponding return options. It has long been
emphasized in this manual page that it is important to call the
procedures described here rather than setting errorInfo or errorCode
directly with Tcl_ObjSetVar2.
If the procedure Tcl_ResetResult is called, it clears all of the state
of the interpreter associated with script evaluation, including the
entire return options dictionary. In particular, the -errorinfo and
-errorcode options are reset. If an error had occurred, the
Tcl_ResetResult call will clear the error state to make it appear as if
no error had occurred after all. The global variables errorInfo and
errorCode are not modified by Tcl_ResetResult so they continue to hold
a record of information about the most recent error seen in an
interpreter.
SEE ALSO
Tcl_DecrRefCount(3), Tcl_IncrRefCount(3), Tcl_Interp(3),
Tcl_ResetResult(3), Tcl_SetErrno(3), errorCode(n), errorInfo(n)
KEYWORDS
error, value, value result, stack, trace, variable
Tcl 8.5 Tcl_AddErrorInfo(3)
tcl 8.6.15 - Generated Tue Dec 3 14:31:52 CST 2024