load(n) Tcl Built-In Commands load(n)
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
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 pack-
age, and is used to compute the name of an initialization procedure.
interp is the path name of the interpreter into which to load the pack-
age (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
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 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
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 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.
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 file-
name which starts with - and you provide a packageName to the load com-
mand.
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 dur-
ing 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 error, it is also possible that a depen-
dent library was not found. To see the dependent libraries,
type 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(n), Tcl_StaticPackage(3), safe(n)
KEYWORDS
binary code, dynamic library, load, safe interpreter, shared library
Tcl 7.5 load(n)
tcl 8.6.0 - Generated Wed Jan 9 19:01:43 CST 2013