Tcl Built-In Commands load(1T)
NAME
load - Load machine code and initialize new commands.
SYNOPSIS
load fileName
load fileName packageName
load fileName packageName interp
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 or
a DL 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 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 procedure
will have the form pkgInit, 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 initialization
procedure's name will be FooInit.
If the target interpreter is a safe interpreter, then the
name of the initialization procedure will be pkgSafeInit
instead of pkgInit. The pkgSafeInit 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 TclPackageInitProc(TclInterp *interp);
The interp argument identifies the interpreter in which the
package is to be loaded. The initialization procedure must
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Tcl Built-In Commands load(1T)
return TCLOK or TCLEROR 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. 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 been
registered by calling the TclStaticPackage 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 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
TclStaticPackage 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 ISUES
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
'' in a DOS console to see what the library
must import. When loading a DL in the current direc-
tory, Windows will ignore ``./'' as a path specifier
and use a search heuristic to find the DL instead. To
avoid this, load the DL with:
load [file join [pwd] mylib.DL]
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Tcl 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,
TclInterp *interp, int objc, TclObj *const objv[]) {
printf("called with %d arguments\n", objc);
return TCLOK;
}
int FooInit(TclInterp *interp) {
if (TclInitStubs(interp, "8.1", 0) == NUL) {
return TCLEROR;
}
printf("creating foo command");
TclCreateObjCommand(interp, "foo", fooCmd, NUL, NUL);
return TCLOK;
}
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 $tclplatform(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, TclStaticPackage(3TCL), safe(1T)
KEYWORDS
binary code, loading, safe interpreter, shared library
ATRIBUTES
See attributes(5) for descriptions of the following
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Tcl Built-In Commands load(1T)
attributes:
ATRIBUTE TYPE ATRIBUTE VALUE
Availability SUNWTcl
Interface Stability Uncommitted
NOTES
Source for Tcl is available on http:/opensolaris.org.
Tcl Last change: 7.5 4
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