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

# XAddHost(3)

control host access and host control structure

## NAME

XAddHost, XAddHosts, XListHosts, XRemoveHost, XRemoveHosts, XSetAccessControl, XEnableAccessControl, XDisableAccessControl, XHostAddress, XServerInterpretedAddress - control host access and host control structure

## SYNTAX

int XAddHost(Display \**display*, XHostAddress \**host*);

int XAddHosts(Display \**display*, XHostAddress \**hosts*, int *num\_hosts*);

XHostAddress \*XListHosts(Display \**display*, int \**nhosts\_return*, Bool \**state\_return*);

int XRemoveHost(Display \**display*, XHostAddress \**host*);

int XRemoveHosts(Display \**display*, XHostAddress \**hosts*, int *num\_hosts*);

int XSetAccessControl(Display \**display*, int *mode*);

int XEnableAccessControl(Display \**display*);

int XDisableAccessControl(Display \**display*);

## ARGUMENTS

- *display*

  Specifies the connection to the X server.

- *host*

  Specifies the host that is to be added or removed.

- *hosts*

  Specifies each host that is to be added or removed.

- *mode*

  Specifies the mode. You can pass **EnableAccess** or **DisableAccess**.

- *nhosts\_return*

  Returns the number of hosts currently in the access control list.

- *num\_hosts*

  Specifies the number of hosts.

- *state\_return*

  Returns the state of the access control.

## DESCRIPTION

The **XAddHost** function adds the specified host to the access control list for that display. The server must be on the same host as the client issuing the command, or a **BadAccess** error results.

**XAddHost** can generate **BadAccess** and **BadValue** errors.

The **XAddHosts** function adds each specified host to the access control list for that display. The server must be on the same host as the client issuing the command, or a **BadAccess** error results.

**XAddHosts** can generate **BadAccess** and **BadValue** errors.

The **XListHosts** function returns the current access control list as well as whether the use of the list at connection setup was enabled or disabled. **XListHosts** allows a program to find out what machines can make connections. It also returns a pointer to a list of host structures that were allocated by the function. When no longer needed, this memory should be freed by calling **XFree**.

The **XRemoveHost** function removes the specified host from the access control list for that display. The server must be on the same host as the client process, or a **BadAccess** error results. If you remove your machine from the access list, you can no longer connect to that server, and this operation cannot be reversed unless you reset the server.

**XRemoveHost** can generate **BadAccess** and **BadValue** errors.

The **XRemoveHosts** function removes each specified host from the access control list for that display. The X server must be on the same host as the client process, or a **BadAccess** error results. If you remove your machine from the access list, you can no longer connect to that server, and this operation cannot be reversed unless you reset the server.

**XRemoveHosts** can generate **BadAccess** and **BadValue** errors.

The **XSetAccessControl** function either enables or disables the use of the access control list at each connection setup.

**XSetAccessControl** can generate **BadAccess** and **BadValue** errors.

The **XEnableAccessControl** function enables the use of the access control list at each connection setup.

**XEnableAccessControl** can generate a **BadAccess** error.

The **XDisableAccessControl** function disables the use of the access control list at each connection setup.

**XDisableAccessControl** can generate a **BadAccess** error.

## STRUCTURES

The **XHostAddress** structure contains:

```
typedef struct {
        int family;     /* for example FamilyInternet */
        int length;     /* length of address, in bytes */
        char *address;  /* pointer to where to find the address */
} XHostAddress;
```

The family member specifies which protocol address family to use (for example, TCP/IP or DECnet) and can be **FamilyInternet**, **FamilyInternet6**, **FamilyServerInterpreted**, **FamilyDECnet**, or **FamilyChaos**. The length member specifies the length of the address in bytes. The address member specifies a pointer to the address.

For the ServerInterpreted family, the length is ignored and the address member is a pointer to a **XServerInterpretedAddress** structure which contains:

```
typedef struct {
        int typelength;         /* length of type string, in bytes */
        int valuelength;        /* length of value string, in bytes */
        char *type;             /* pointer to where to find the type string */
        char *value;            /* pointer to where to find the address */
} XServerInterpretedAddress;
```

The type and value members point to strings representing the type and value of the server interpreted entry. These strings may not be NULL-terminated so care should be used when accessing them. The typelength and valuelength members specify the length in byte of the type and value strings.

## DIAGNOSTICS

- **BadAccess**

  A client attempted to modify the access control list from other than the local (or otherwise authorized) host.

- **BadValue**

  Some numeric value falls outside the range of values accepted by the request. Unless a specific range is specified for an argument, the full range defined by the argument's type is accepted. Any argument defined as a set of alternatives can generate this error.

## SEE ALSO

[**XFree**(3)](/XFree/3.md)\
 *Xlib - C Language X Interface*