---
name: "Tcl_RegisterConfig"
section: "3"
platform: "linux"
package: "tcl"
version: "8.6.16-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/Tcl_RegisterConfig"
---

# Tcl\_RegisterConfig(3)

procedures to register embedded configuration information

```

```

## 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.

  ```

  ```

## 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