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

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NAME

       load - Load machine code and initialize new commands

SYNOPSIS

       load fileName
       load fileName packageName
       load 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  com-
       mand  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 cur-
              rent 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
", 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)