load(3tcl)


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
   address space and calls an initialization procedure in the  package  to
   incorporate  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
   Solaris 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.
   Typically  the  initialization procedure will add new commands to a Tcl
   interpreter.  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
   initializes  the  safe  interpreter  only  with  partial  functionality
   provided by the package that is safe for use  by  untrusted  code.  For
   more information 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
   returned 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
   interpreters, then the first load will  load  the  code  and  call  the
   initialization    procedure;     subsequent   loads   will   call   the
   initialization procedure 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 mechanism.

   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
   different  platforms.   The  default  guess, which is used on most UNIX
   platforms, 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
   different 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
          dependent  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(3tcl), safe(3tcl)

KEYWORDS

   binary code, loading, safe interpreter, shared library





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