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error(3tcl)


NAME

   error - Generate an error

SYNOPSIS

   error message ?info? ?code?
______________________________________________________________________________

DESCRIPTION

   Returns  a  TCL_ERROR  code,  which causes command interpretation to be
   unwound.  Message is a string that is returned to  the  application  to
   indicate what went wrong.

   The  -errorinfo return option of an interpreter is used to accumulate a
   stack trace of what was in progress when an error occurred;  as  nested
   commands unwind, the Tcl interpreter adds information to the -errorinfo
   return option.  If  the  info  argument  is  present,  it  is  used  to
   initialize  the  -errorinfo  return  options and the first increment of
   unwind information will not be added by the Tcl interpreter.  In  other
   words,  the command containing the error command will not appear in the
   stack trace; in its place will be info.  Historically, this feature had
   been  most  useful  in  conjunction with the catch command: if a caught
   error cannot be handled successfully, info can  be  used  to  return  a
   stack trace reflecting the original point of occurrence of the error:
          catch {...} errMsg
          set savedInfo $::errorInfo
          ...
          error $errMsg $savedInfo
   When  working  with Tcl 8.5 or later, the following code should be used
   instead:
          catch {...} errMsg options
          ...
          return -options $options $errMsg

   If the code argument is present,  then  its  value  is  stored  in  the
   -errorcode  return option.  The -errorcode return option is intended to
   hold a machine-readable description of the error in  cases  where  such
   information is available; see the return manual page for information on
   the proper format for this option's value.

EXAMPLE

   Generate an error if a basic mathematical operation fails:
          if {1+2 != 3} {
              error "something is very wrong with addition"
          }

SEE ALSO

   catch(3tcl), return(3tcl)

KEYWORDS

   error



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