Tcl_InitStubs(3) Tcl Library Procedures Tcl_InitStubs(3)______________________________________________________________________________NAME
Tcl_InitStubs - initialize the Tcl stubs mechanism
Tcl_InitStubs(interp, version, exact)
Tcl_Interp *interp (in) Tcl interpreter handle.
char *version (in) A version string consisting of one or
more decimal numbers separated by
int exact (in) Non-zero means that only the particu‐
lar version specified by version is
acceptable. Zero means that versions
newer than version are also acceptable
as long as they have the same major
version number as version.
The Tcl stubs mechanism defines a way to dynamically bind extensions to
a particular Tcl implementation at run time. This provides two signif‐
icant benefits to Tcl users:
1) Extensions that use the stubs mechanism can be loaded into multi‐
ple versions of Tcl without being recompiled or relinked.
2) Extensions that use the stubs mechanism can be dynamically loaded
into statically-linked Tcl applications.
The stubs mechanism accomplishes this by exporting function tables that
define an interface to the Tcl API. The extension then accesses the
Tcl API through offsets into the function table, so there are no direct
references to any of the Tcl library's symbols. This redirection is
transparent to the extension, so an extension writer can continue to
use all public Tcl functions as documented.
The stubs mechanism requires no changes to applications incorporating
Tcl interpreters. Only developers creating C-based Tcl extensions need
to take steps to use the stubs mechanism with their extensions.
Enabling the stubs mechanism for an extension requires the following
1) Call Tcl_InitStubs in the extension before calling any other Tcl
2) Define the USE_TCL_STUBS symbol. Typically, you would include the
-DUSE_TCL_STUBS flag when compiling the extension.
3) Link the extension with the Tcl stubs library instead of the stan‐
dard Tcl library. On Unix platforms, the library name is libt‐
clstub8.1.a; on Windows platforms, the library name is
If the extension also requires the Tk API, it must also call Tk_Init‐
Stubs to initialize the Tk stubs interface and link with the Tk stubs
libraries. See the Tk_InitStubs page for more information.
Tcl_InitStubs attempts to initialize the stub table pointers and ensure
that the correct version of Tcl is loaded. In addition to an inter‐
preter handle, it accepts as arguments a version number and a Boolean
flag indicating whether the extension requires an exact version match
or not. If exact is 0, then the extension is indicating that newer
versions of Tcl are acceptable as long as they have the same major ver‐
sion number as version; non-zero means that only the specified version
is acceptable. Tcl_InitStubs returns a string containing the actual
version of Tcl satisfying the request, or NULL if the Tcl version is
not acceptable, does not support stubs, or any other error condition
Tcl 8.1 Tcl_InitStubs(3)