Provided by: tcl8.6-doc_8.6.9+dfsg-2_all bug

NAME

       load - Load machine code and initialize new commands

SYNOPSIS

       load ?-global? ?-lazy? ?--? fileName
       load ?-global? ?-lazy? ?--? fileName packageName
       load ?-global? ?-lazy? ?--? fileName packageName interp
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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.

       If  -global  is  specified preceding the filename, all symbols found in the shared library
       are exported for global use by other libraries. The option -lazy delays the actual loading
       of  symbols  until  their first actual use. The options may be abbreviated.  The option --
       indicates the end of the options, and should be used if you wish to use a  filename  which
       starts with - and you provide a packageName to the load command.

       On  platforms  which  do not support the -global or -lazy options, the options still exist
       but have no effect. Note that use of the -global or -lazy option may lead  to  crashes  in
       your  application  later (in case of symbol conflicts resp. missing symbols), which cannot
       be detected during the load. So, only use this when you know what you are doing, you  will
       not get a nice error message when something is wrong with the loaded library.

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, package(3tcl), Tcl_StaticPackage(3tcl), safe(3tcl)

KEYWORDS

       binary code, dynamic library, load, safe interpreter, shared library