Tcl_RegisterConfig(3) Tcl Library Procedures Tcl_RegisterConfig(3)

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NAME

Tcl_RegisterConfig - procedures to register embedded configuration
information

SYNOPSIS

#include <tcl.h>

void
Tcl_RegisterConfig(interp, pkgName, configuration, valEncoding)

ARGUMENTS

Tcl_Interp *interp (in) Refers to the interpreter the
embedded configuration
information is registered
for. Must not be NULL.

const char *pkgName (in) Contains the name of the
package registering the
embedded configuration as
ASCII string. This means that
this information is in UTF-8
too. Must not be NULL.

const Tcl_Config *configuration (in) Refers to an array of
Tcl_Config entries containing
the information embedded in
the binary library. Must not
be NULL. The end of the array
is signaled by either a key
identical to NULL, or a key
referring to the empty
string.

const char *valEncoding (in) Contains the name of the
encoding used to store the
configuration values as ASCII
string. This means that this
information is in UTF-8 too.
Must not be NULL.
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DESCRIPTION

The function described here has its base in TIP 59 and provides
extensions with support for the embedding of configuration
information into their binary library and the generation of a Tcl-
level interface for querying this information.

To embed configuration information into their binary library an
extension has to define a non-volatile array of Tcl_Config entries in
one if its source files and then call Tcl_RegisterConfig to register
that information.

Tcl_RegisterConfig takes four arguments; first, a reference to the
interpreter we are registering the information with, second, the name
of the package registering its configuration information, third, a
pointer to an array of structures, and fourth a string declaring the
encoding used by the configuration values.

The string valEncoding contains the name of an encoding known to Tcl.
All these names are use only characters in the ASCII subset of UTF-8
and are thus implicitly in the UTF-8 encoding. It is expected that
keys are legible English text and therefore using the ASCII subset of
UTF-8. In other words, they are expected to be in UTF-8 too. The
values associated with the keys can be any string however. For these
the contents of valEncoding define which encoding was used to
represent the characters of the strings.

Each element of the configuration array refers to two strings
containing the key and the value associated with that key. The end of
the array is signaled by either an empty key or a key identical to
NULL. The function makes no copy of the configuration array. This
means that the caller has to make sure that the memory holding this
array is never released. This is the meaning behind the word non-
volatile used earlier. The easiest way to accomplish this is to
define a global static array of Tcl_Config entries. See the file
"generic/tclPkgConfig.c" in the sources of the Tcl core for an
example.

When called Tcl_RegisterConfig will

(1) create a namespace having the provided pkgName, if not yet
existing.

(2) create the command pkgconfig in that namespace and link it to
the provided information so that the keys from configuration
and their associated values can be retrieved through calls to
pkgconfig.

The command pkgconfig will provide two subcommands, list and get:

::pkgName::pkgconfig list
Returns a list containing the names of all defined
keys.

::pkgName::pkgconfig get key
Returns the configuration value associated with the
specified key.

TCL_CONFIG
The Tcl_Config structure contains the following fields:

typedef struct Tcl_Config {
const char *key;
const char *value;
} Tcl_Config;

KEYWORDS

embedding, configuration, binary library

Tcl 8.4 Tcl_RegisterConfig(3)