Tcl Built-In Commands load(1T)
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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 pro-
cedure 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 ora 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 intowhich to load the package (see the interp manual entry for
details); if interp is omitted, it defaults to the inter-
preter 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 procedurewill have the form pkg_Init, where pkg is the same as pack-
ageName 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 initializationprocedure's name will be Foo_Init.
If the target interpreter is a safe interpreter, then thename 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 inter-
preter only with partial functionality provided by the pack-
age that is safe for use by untrusted code. For more infor-
mation on Safe-Tcl, see the safe manual entry.
The initialization procedure must match the following proto-
type:typedef int Tcl_PackageInitProc(Tcl_Interp *interp);
The interp argument identifies the interpreter in which thepackage is to be loaded. The initialization procedure must
Tcl Last change: 7.5 1Tcl Built-In Commands load(1T)
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; subsequentloads will call the initialization procedure without loading
the code again. It is not possible to unload or reload a
package.The load command also supports packages that are statically
linked with the application, if those packages have beenregistered by calling the Tcl_StaticPackage procedure. If
fileName is an empty string, then packageName must be speci-
fied. 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 commandload 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 WindowsWhen 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
'' in a DOS console to see what the library must import. When loading a DLL in the current direc-
tory, Windows will ignore ``./'' as a path specifier and use a search heuristic to find the DLL instead. Toavoid this, load the DLL with:
load [file join [pwd] mylib.DLL]
Tcl Last change: 7.5 2Tcl Built-In Commands load(1T)
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 sys-
tems may detect the redundant loads, others may not).
EXAMPLE
The following is a minimal extension:#include
#include
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 andLinux) 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
fooSEE ALSO
info sharedlibextension, Tcl_StaticPackage(3TCL), safe(1T)
KEYWORDSbinary code, loading, safe interpreter, shared library
ATTRIBUTES
See attributes(5) for descriptions of the following Tcl Last change: 7.5 3Tcl Built-In Commands load(1T)
attributes:_______________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE|
|____________________|__________________|_
| Availability | runtime/tcl-8 |
|____________________|__________________|_
| Interface Stability| Uncommitted ||____________________|_________________|
NOTES Source for Tcl is available on http://opensolaris.org. Tcl Last change: 7.5 4