---
name: "XkbAllocCompatMap"
section: "3"
platform: "linux"
package: "libx11"
version: "1.8.14-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/XkbAllocCompatMap"
---

# XkbAllocCompatMap(3)

Allocate a new compatibility map if you do not already have one available

## NAME

XkbAllocCompatMap - Allocate a new compatibility map if you do not already have one available

## SYNOPSIS

**Status XkbAllocCompatMap** **(XkbDescPtr** *xkb***,** **unsigned int** *which***,** **unsigned int** *num\_si***);**

## ARGUMENTS

- *xkb*

  keyboard description in which to allocate compat map

- *which*

  mask of compatibility map components to allocate

- *num\_si*

  number of symbol interpretations to allocate

## DESCRIPTION

*xkb* specifies the keyboard description for which compatibility maps are to be allocated. The compatibility map is the *compat* field in this structure.

*which* specifies the compatibility map components to be allocated (see XkbGetCompatMap). *which* is an inclusive OR of the bits shown in Table 1.

| | | |
| --- | --- | --- |
| Table 1 Compatibility Map Component Masks |
| Mask | Value | Affecting |
| XkbSymInterpMask | (1\<\<0) | Symbol interpretations |
| XkbGroupCompatMask | (1\<\<1) | Group maps |
| XkbAllCompatMask | (0x3) | All compatibility map components |

*num\_si* specifies the total number of entries to allocate in the symbol interpretation vector *(xkb.compat.sym\_interpret).*

*XkbAllocCompatMap* returns Success if successful, BadMatch if *xkb* is NULL, or BadAlloc if errors are encountered when attempting to allocate storage.

## STRUCTURES

```
    typedef struct {
        KeySym            sym;          /* keysym of interest or NULL */
        unsigned char     flags;        /* XkbSI_AutoRepeat, XkbSI_LockingKey */
        unsigned char     match;        /* specifies how mods is interpreted */
        unsigned char     mods;         /* modifier bits, correspond to eight real modifiers */
        unsigned char     virtual_mod;  /* 1 modifier to add to key virtual mod map */
        XkbAnyAction      act;          /* action to bind to symbol position on key */
    } XkbSymInterpretRec,*XkbSymInterpretPtr;
```

## DIAGNOSTICS

- **BadAlloc**

  Unable to allocate storage

- **BadMatch**

  A compatible version of Xkb was not available in the server or an argument has correct type and range, but is otherwise invalid

## SEE ALSO

[**XkbGetCompatMap**(3)](/XkbGetCompatMap/3.md)

## NOTES

Note that symbol interpretations in a compatibility map (the *sym\_interpret* vector of XkbSymInterpretRec structures) are also allocated using this same function. To ensure that there is sufficient space in the symbol interpretation vector for entries to be added, use *XkbAllocCompatMap* specifying *which* as XkbSymInterpretMask and the number of free symbol interpretations needed in *num\_si.*