---
name: "XtSetArg"
section: "3"
platform: "linux"
package: "libxt"
version: "1.3.1-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/XtSetArg"
---

# XtSetArg(3)

set and merge ArgLists

## NAME

XtSetArg, XtMergeArgLists - set and merge ArgLists

## SYNTAX

\#include \<X11/Intrinsic.h\>

int XtSetArg(Arg *arg*, String *name*, XtArgVal *value*);

ArgList XtMergeArgLists(ArgList *args1*, Cardinal *num\_args1*, ArgList *args2*, Cardinal *num\_args2*);

## ARGUMENTS

- *arg*

  Specifies the name-value pair to set.

- *args1*

  Specifies the first **ArgList**.

- *args2*

  Specifies the second **ArgList**.

- *num\_args1*

  Specifies the number of arguments in the first argument list.

- *num\_args2*

  Specifies the number of arguments in the second argument list.

- *name*

  Specifies the name of the resource.

- *value*

  Specifies the value of the resource if it will fit in an **XtArgVal** or the address.

## DESCRIPTION

The **XtSetArg** function is usually used in a highly stylized manner to minimize the probability of making a mistake; for example:

```
Arg args[20];
int n;
n = 0;
XtSetArg(args[n], XtNheight, 100);      n++;
XtSetArg(args[n], XtNwidth, 200);       n++;
XtSetValues(widget, args, n);
```

Alternatively, an application can statically declare the argument list and use **XtNumber**:

```
static Args args[] = {
        {XtNheight, (XtArgVal) 100},
        {XtNwidth, (XtArgVal) 200},
};
XtSetValues(Widget, args, XtNumber(args));
```

Note that you should not use auto-increment or auto-decrement within the first argument to **XtSetArg**. **XtSetArg** can be implemented as a macro that dereferences the first argument twice.

The **XtMergeArgLists** function allocates enough storage to hold the combined **ArgList** structures and copies them into it. Note that it does not check for duplicate entries. When it is no longer needed, free the returned storage by using **XtFree**.

## SEE ALSO

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