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load(n)			     Tcl Built-In Commands		       load(n)

______________________________________________________________________________

NAME
       load - Load machine code	and initialize new commands

SYNOPSIS
       load fileName
       load fileName packageName
       load fileName packageName interp
______________________________________________________________________________

DESCRIPTION
       This  command  loads binary code	from a file into the application's ad-
       dress space and calls an	initialization procedure in the	package	to in-
       corporate  it  into  an	interpreter.  fileName is the name of the file
       containing the code;  its exact form varies from	system to  system  but
       on  most	 systems  it is	a shared library, such as a .so	file under So-
       laris or	a DLL under Windows.  packageName is the name of the  package,
       and is used to compute the name of an initialization procedure.	interp
       is the path name	of the interpreter into	which to load the package (see
       the interp manual entry for details); if	interp is omitted, it defaults
       to the interpreter in which the load command was	invoked.

       Once the	file has been loaded into the application's address space, one
       of two initialization procedures	will be	invoked	in the new code.  Typ-
       ically the initialization procedure will	add new	commands to a Tcl  in-
       terpreter.   The	 name of the initialization procedure is determined by
       packageName and whether or not the target interpreter is	 a  safe  one.
       For  normal  interpreters the name of the initialization	procedure will
       have the	form pkg_Init, where pkg is the	 same  as  packageName	except
       that  the first letter is converted to upper case and all other letters
       are converted to	lower case.  For example, if  packageName  is  foo  or
       FOo, the	initialization procedure's name	will be	Foo_Init.

       If  the	target interpreter is a	safe interpreter, then the name	of the
       initialization procedure	will be	pkg_SafeInit instead of	pkg_Init.  The
       pkg_SafeInit  function should be	written	carefully, so that it initial-
       izes the	safe interpreter only with partial functionality  provided  by
       the  package  that is safe for use by untrusted code. For more informa-
       tion on Safe-Tcl, see the safe manual entry.

       The initialization procedure must match the following prototype:
	      typedef int Tcl_PackageInitProc(Tcl_Interp *interp);
       The interp argument identifies the interpreter in which the package  is
       to  be  loaded.	 The  initialization  procedure	 must return TCL_OK or
       TCL_ERROR to indicate whether or	not it completed successfully;	in the
       event of	an error it should set the interpreter's result	to point to an
       error message.  The result of the load command will be the  result  re-
       turned by the initialization procedure.

       The  actual  loading of a file will only	be done	once for each fileName
       in an application.  If a	given fileName is loaded into multiple	inter-
       preters,	 then  the first load will load	the code and call the initial-
       ization procedure;  subsequent loads will call the initialization  pro-
       cedure  without	loading	 the  code again.  For Tcl versions lower than |
       8.5, it is not possible to unload or reload a package. From version 8.5 |
       however,	 the  unload  command allows the unloading of libraries	loaded |
       with load, for libraries	that are aware of the Tcl's  unloading	mecha- |
       nism.

       The load	command	also supports packages that are	statically linked with
       the application,	if those packages have been registered by calling  the
       Tcl_StaticPackage  procedure.   If  fileName  is	 an empty string, then
       packageName must	be specified.

       If packageName is omitted or specified as an empty string, Tcl tries to
       guess the name of the package.  This may	be done	differently on differ-
       ent platforms.  The default guess, which	is used	 on  most  UNIX	 plat-
       forms,  is  to  take  the last element of fileName, strip off the first
       three characters	if they	are lib, and use any following alphabetic  and
       underline characters as the module name.	 For example, the command load
       libxyz4.2.so uses the module name xyz and the command load  bin/last.so
       {} uses the module name last.

       If  fileName  is	 an  empty string, then	packageName must be specified.
       The load	command	first searches for a statically	 loaded	 package  (one
       that has	been registered	by calling the Tcl_StaticPackage procedure) by
       that name; if one is found, it is used.	Otherwise,  the	 load  command
       searches	 for a dynamically loaded package by that name,	and uses it if
       it is found.  If	several	different files	have been loaded with  differ-
       ent versions of the package, Tcl	picks the file that was	loaded first.

PORTABILITY ISSUES
       Windows
	      When  a  load  fails  with "library not found" error, it is also
	      possible that a dependent	library	was not	found.	To see the de-
	      pendent  libraries,  type	 "dumpbin -imports <dllname>" in a DOS
	      console to see what the library must import.  When loading a DLL
	      in  the  current	directory,  Windows will ignore	"./" as	a path
	      specifier	and use	a search heuristic to find  the	 DLL  instead.
	      To avoid this, load the DLL with:
	      load [file join [pwd] mylib.DLL]

BUGS
       If  the	same  file is loaded by	different fileNames, it	will be	loaded
       into the	process's address space	multiple times.	 The behavior of  this
       varies  from  system  to	 system	(some systems may detect the redundant
       loads, others may not).

EXAMPLE
       The following is	a minimal extension:

	      #include <tcl.h>
	      #include <stdio.h>
	      static int fooCmd(ClientData clientData,
		      Tcl_Interp *interp, int objc, Tcl_Obj *const objv[]) {
		  printf("called with %d arguments\n", objc);
		  return TCL_OK;
	      }
	      int Foo_Init(Tcl_Interp *interp) {
		  if (Tcl_InitStubs(interp, "8.1", 0) == NULL) {
		return TCL_ERROR;
		  }
		  printf("creating foo command");
		  Tcl_CreateObjCommand(interp, "foo", fooCmd, NULL, NULL);
		  return TCL_OK;
	      }

       When built into a shared/dynamic	library	with  a	 suitable  name	 (e.g.
       foo.dll	on  Windows,  libfoo.so	 on  Solaris and Linux)	it can then be
       loaded into Tcl with the	following:

	      #	Load the extension
	      switch $tcl_platform(platform) {
		 windows {
		    load [file join [pwd] foo.dll]
		 }
		 unix {
		    load [file join [pwd] libfoo[info sharedlibextension]]
		 }
	      }

	      #	Now execute the	command	defined	by the extension
	      foo

SEE ALSO
       info sharedlibextension,	Tcl_StaticPackage(3), safe(n)

KEYWORDS
       binary code, loading, safe interpreter, shared library

Tcl				      7.5			       load(n)

NAME | SYNOPSIS | DESCRIPTION | PORTABILITY ISSUES | BUGS | EXAMPLE | SEE ALSO | KEYWORDS

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