NAME

       Tcl_AddObjErrorInfo,      Tcl_AddErrorInfo,     Tcl_SetObjErrorCode,     Tcl_SetErrorCode,
       Tcl_SetErrorCodeVA, Tcl_PosixError, 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  contain
                                         embedded  null  bytes  unless  length  is negative.  For
                                         Tcl_AddErrorInfo, this is a  conventional  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 initialized  using
                                         TCL_VARARGS_START, and cleared using va_end.

       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

       These procedures are used to manipulate two Tcl global  variables  that  hold  information
       about  errors.   The variable 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 various 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_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_EvalObjEx.   Tcl_AddObjErrorInfo  may  be  used  for this
       purpose: its message and length arguments describe an additional string to be appended  to
       errorInfo.   For  example, 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_AddObjErrorInfo 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_SetErrorCode
       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 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 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
       errorInfo  variable,  and the line number stored internally in the interpreter is set.  On
       the first call to Tcl_LogCommandInfo 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 procedures 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 message.  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_ResetResult, Tcl_SetErrno

KEYWORDS

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