DOKK / manpages / debian 11 / tcl8.6-doc / Tcl_RegisterConfig.3tcl.en
Tcl_RegisterConfig(3tcl) Tcl Library Procedures Tcl_RegisterConfig(3tcl) 







Tcl_RegisterConfig - procedures to register embedded configuration
    information








#include <tcl.h>

void
Tcl_RegisterConfig(interp, pkgName, configuration, valEncoding)











  
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.
    
    

    

  










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.












The Tcl_Config structure contains the following fields:






typedef struct Tcl_Config {


    const char *key;


    const char *value;
} Tcl_Config;










embedding, configuration, binary library







  

    8.4
    Tcl