load

load(3tcl)                   Tcl Built-In Commands                  load(3tcl)



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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



Tcl                                   7.5                           load(3tcl)