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Tcl_Panic(3)		     Tcl Library Procedures		    Tcl_Panic(3)

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NAME
     Tcl_Panic, Tcl_PanicVA, Tcl_SetPanicProc - report fatal error and abort

SYNOPSIS
     #include <tcl.h>

     void
     Tcl_Panic(format, arg, arg, ...)

     void
     Tcl_PanicVA(format, argList)

     void
     Tcl_SetPanicProc(panicProc)

ARGUMENTS
     const char* format (in)		    A printf-style format string.

      arg (in)				    Arguments	 matching   the   format
					    string.

     va_list argList (in)		    An argument list of arguments match-
					    ing the format  string.   Must  have
					    been initialized using va_start, and
					    cleared using va_end.

     Tcl_PanicProc *panicProc (in)	    Procedure to report fatal error mes-
					    sage and abort.
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DESCRIPTION
     When  the	Tcl  library detects that its internal data structures are in an
     inconsistent state, or that its C procedures have been called in  a  manner
     inconsistent with their documentation, it calls Tcl_Panic to display a mes-
     sage  describing the error and abort the process.	The format argument is a
     format string describing how to format the remaining arguments arg into  an
     error  message,  according  to the same formatting rules used by the printf
     family of functions.  The same formatting rules are also used by the built-
     in Tcl command format.

     In a freshly loaded Tcl library, Tcl_Panic prints the formatted error  mes-
     sage  to  the  standard  error file of the process, and then calls abort to
     terminate the process.  Tcl_Panic does not return. On Windows, when  a  de-
     bugger  is running, the formatted error message is sent to the debugger in-
     stead. If the windows executable does  not  have  a  stderr  channel  (e.g.
     wish.exe), then a system dialog box is used to display the panic message.

     Tcl_SetPanicProc may be used to modify the behavior of Tcl_Panic.	The pan-
     icProc argument should match the type Tcl_PanicProc:

	    typedef void Tcl_PanicProc(
		    const char *format,
		    arg, arg,...);

     After  Tcl_SetPanicProc  returns,	any  future calls to Tcl_Panic will call
     panicProc, passing along the format and  arg  arguments.  panicProc  should
     avoid  making  calls into the Tcl library, or into other libraries that may
     call the Tcl library, since the original call to  Tcl_Panic  indicates  the
     Tcl library is not in a state of reliable operation.

     The  typical  use	of Tcl_SetPanicProc arranges for the error message to be
     displayed or reported in a manner more suitable for the application or  the
     platform.

     Although the primary callers of Tcl_Panic are the procedures of the Tcl li-
     brary, Tcl_Panic is a public function and may be called by any extension or
     application  that wishes to abort the process and have a panic message dis-
     played the same way that panic messages from Tcl will be displayed.

     Tcl_PanicVA is the same as Tcl_Panic except that instead of taking a  vari-
     able number of arguments it takes an argument list.

SEE ALSO
     abort(3), printf(3), exec(n), format(n)

KEYWORDS
     abort, fatal, error

Tcl				       8.4			    Tcl_Panic(3)

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