1load(n) Tcl Built-In Commands load(n)
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8 load - Load machine code and initialize new commands
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11 load fileName
12 load fileName packageName
13 load fileName packageName interp
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18 This command loads binary code from a file into the application's
19 address space and calls an initialization procedure in the package to
20 incorporate it into an interpreter. fileName is the name of the file
21 containing the code; its exact form varies from system to system but
22 on most systems it is a shared library, such as a .so file under
23 Solaris or a DLL under Windows. packageName is the name of the pack‐
24 age, and is used to compute the name of an initialization procedure.
25 interp is the path name of the interpreter into which to load the pack‐
26 age (see the interp manual entry for details); if interp is omitted, it
27 defaults to the interpreter in which the load command was invoked.
28 Once the file has been loaded into the application's address space, one
30 of two initialization procedures will be invoked in the new code. Typ‐
31 ically the initialization procedure will add new commands to a Tcl
32 interpreter. The name of the initialization procedure is determined by
33 packageName and whether or not the target interpreter is a safe one.
34 For normal interpreters the name of the initialization procedure will
35 have the form pkg_Init, where pkg is the same as packageName except
36 that the first letter is converted to upper case and all other letters
37 are converted to lower case. For example, if packageName is foo or
38 FOo, the initialization procedure's name will be Foo_Init.
39 If the target interpreter is a safe interpreter, then the name of the
41 initialization procedure will be pkg_SafeInit instead of pkg_Init. The
42 pkg_SafeInit function should be written carefully, so that it initial‐
43 izes the safe interpreter only with partial functionality provided by
44 the package that is safe for use by untrusted code. For more informa‐
45 tion on Safe-Tcl, see the safe manual entry.
46 The initialization procedure must match the following prototype:
48 typedef int Tcl_PackageInitProc(Tcl_Interp *interp);
49 The interp argument identifies the interpreter in which the package is
50 to be loaded. The initialization procedure must return TCL_OK or
51 TCL_ERROR to indicate whether or not it completed successfully; in the
52 event of an error it should set the interpreter's result to point to an
53 error message. The result of the load command will be the result
54 returned by the initialization procedure.
55 The actual loading of a file will only be done once for each fileName
57 in an application. If a given fileName is loaded into multiple inter‐
58 preters, then the first load will load the code and call the initial‐
59 ization procedure; subsequent loads will call the initialization pro‐
60 cedure without loading the code again. For Tcl versions lower than │
61 8.5, it is not possible to unload or reload a package. From version 8.5 │
62 however, the unload command allows the unloading of libraries loaded │
63 with load, for libraries that are aware of the Tcl's unloading mecha‐ │
64 nism.
65 The load command also supports packages that are statically linked with
67 the application, if those packages have been registered by calling the
68 Tcl_StaticPackage procedure. If fileName is an empty string, then
69 packageName must be specified.
70 If packageName is omitted or specified as an empty string, Tcl tries to
72 guess the name of the package. This may be done differently on differ‐
73 ent platforms. The default guess, which is used on most UNIX plat‐
74 forms, is to take the last element of fileName, strip off the first
75 three characters if they are lib, and use any following alphabetic and
76 underline characters as the module name. For example, the command load
77 libxyz4.2.so uses the module name xyz and the command load bin/last.so
78 {} uses the module name last.
79 If fileName is an empty string, then packageName must be specified.
81 The load command first searches for a statically loaded package (one
82 that has been registered by calling the Tcl_StaticPackage procedure) by
83 that name; if one is found, it is used. Otherwise, the load command
84 searches for a dynamically loaded package by that name, and uses it if
85 it is found. If several different files have been loaded with differ‐
86 ent versions of the package, Tcl picks the file that was loaded first.
87
89 Windows
90 When a load fails with “library not found” error, it is also
91 possible that a dependent library was not found. To see the
92 dependent libraries, type “dumpbin -imports <dllname>” in a DOS
93 console to see what the library must import. When loading a DLL
94 in the current directory, Windows will ignore “./” as a path
95 specifier and use a search heuristic to find the DLL instead.
96 To avoid this, load the DLL with:
97 load [file join [pwd] mylib.DLL]
98
100 If the same file is loaded by different fileNames, it will be loaded
101 into the process's address space multiple times. The behavior of this
102 varies from system to system (some systems may detect the redundant
103 loads, others may not).
104
106 The following is a minimal extension:
107 #include <tcl.h>
109 #include <stdio.h>
110 static int fooCmd(ClientData clientData,
111 Tcl_Interp *interp, int objc, Tcl_Obj *const objv[]) {
112 printf("called with %d arguments\n", objc);
113 return TCL_OK;
114 }
115 int Foo_Init(Tcl_Interp *interp) {
116 if (Tcl_InitStubs(interp, "8.1", 0) == NULL) {
117 return TCL_ERROR;
118 }
119 printf("creating foo command");
120 Tcl_CreateObjCommand(interp, "foo", fooCmd, NULL, NULL);
121 return TCL_OK;
122 }
123 When built into a shared/dynamic library with a suitable name (e.g.
125 foo.dll on Windows, libfoo.so on Solaris and Linux) it can then be
126 loaded into Tcl with the following:
127 # Load the extension
129 switch $tcl_platform(platform) {
130 windows {
131 load [file join [pwd] foo.dll]
132 }
133 unix {
134 load [file join [pwd] libfoo[info sharedlibextension]]
135 }
136 }
137 # Now execute the command defined by the extension
139 foo
140
143 info sharedlibextension, Tcl_StaticPackage(3), safe(n)
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147 binary code, loading, safe interpreter, shared library
148Tcl 7.5 load(n)