---
name: "Tk_SetClassProcs"
section: "3tk"
platform: "linux"
package: "tk8.6-doc"
version: "8.6.16-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/Tk_SetClassProcs/3tk"
---

# Tk\_SetClassProcs(3tk)

register widget specific procedures

```

```

## NAME

Tk\_SetClassProcs - register widget specific procedures

## SYNOPSIS

```
#include <tk.h>

Tk_SetClassProcs(tkwin, procs, instanceData)
```

## ARGUMENTS

- Tk\_Window *tkwin* (in)

  Token for window to modify.

- const Tk\_ClassProcs *\*procs* (in)

  Pointer to data structure containing widget specific procedures. The data structure pointed to by *procs* must be static: Tk keeps a reference to it as long as the window exists.

- ClientData *instanceData* (in)

  Arbitrary one-word value to pass to widget callbacks.

  ```

  ```

## DESCRIPTION

**Tk\_SetClassProcs** is called to register a set of procedures that are used as callbacks in different places.

The structure pointed to by *procs* contains the following:

```
typedef struct Tk_ClassProcs {
    unsigned int size;
    Tk_ClassWorldChangedProc *worldChangedProc;
    Tk_ClassCreateProc *createProc;
    Tk_ClassModalProc *modalProc;
} Tk_ClassProcs;
```

The *size* field is used to simplify future expansion of the structure. It should always be set to (literally) **sizeof(Tk\_ClassProcs)**.

*worldChangedProc* is invoked when the system has altered in some way that requires some reaction from the widget.  For example, when a font alias (see the **font** manual entry) is reconfigured, widgets configured to use that font alias must update their display accordingly.  *worldChangedProc* should have arguments and results that match the type **Tk\_ClassWorldChangedProc**:

```
typedef void Tk_ClassWorldChangedProc(
        ClientData instanceData);
```

The *instanceData* parameter passed to the *worldChangedProc* will be identical to the *instanceData* parameter passed to **Tk\_SetClassProcs**.

*createProc* is used to create platform-dependent windows.  It is invoked by **Tk\_MakeWindowExist**.  *createProc* should have arguments and results that match the type **Tk\_ClassCreateProc**:

```
typedef Window Tk_ClassCreateProc(
        Tk_Window tkwin,
        Window parent,
        ClientData instanceData);
```

The *tkwin* and *instanceData* parameters will be identical to the *tkwin* and *instanceData* parameters passed to **Tk\_SetClassProcs**.  The *parent* parameter will be the parent of the window to be created.  The *createProc* should return the created window.

*modalProc* is invoked after all bindings on a widget have been triggered in order to handle a modal loop.  *modalProc* should have arguments and results that match the type **Tk\_ClassModalProc**:

```
typedef void Tk_ClassModalProc(
        Tk_Window tkwin,
        XEvent *eventPtr);
```

The *tkwin* parameter to *modalProc* will be identical to the *tkwin* parameter passed to **Tk\_SetClassProcs**.  The *eventPtr* parameter will be a pointer to an XEvent structure describing the event being processed.

## KEYWORDS

callback, class