tcl_adderrorinfo(3)

NAME

Tcl_AddObjErrorInfo, Tcl_AddErrorInfo, Tcl_SetObjError
Code, Tcl_SetErrorCode, Tcl_SetErrorCodeVA, Tcl_PosixEr
ror, Tcl_LogCommandInfo - 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

Tcl_SetErrorCodeVA(interp, argList)

CONST char *
Tcl_PosixError(interp)

void
Tcl_LogCommandInfo(interp, script, command, commandLength)

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.
va_list argList (in) An argument list which: must have been initial
ized using
TCL_VARARGS_START, and cleared using va_end.
CONST char *script (in) Pointer to first charac: ter in script containing
command (must be <= com
mand)
CONST char *command (in) Pointer to first charac: ter in command that gen
erated the error
int commandLength(in) Number of bytes in com: mand; -1 means use all
bytes up to first NULL
byte

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_EvalObjEx (or Tcl_Eval, which calls Tcl_EvalObjEx) it calls the procedure Tcl_AddObjEr rorInfo 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_EvalObjEx. 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_EvalObjEx 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
information 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_SetErrorCodeVA is the same as Tcl_SetErrorCode except that instead of taking a variable number of arguments it
takes an argument list.

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.

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 error
Info variable, and the line number stored internally in
the interpreter is set. On the first call to Tcl_LogCom mandInfo or Tcl_AddObjErrorInfo since an error occurred, the old information in errorInfo is deleted.

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.

KEYWORDS

error, object, object result, stack, trace, variable

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