---
name: "VistaIOSetWarningHandler"
section: "3"
platform: "linux"
package: "libvistaio-dev"
version: "1.2.19-3+b2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/VistaIOSetWarningHandler"
---

# VistaIOSetWarningHandler(3)

register a procedure to be called on any nonfatal error

## NAME

VistaIOSetWarningHandler - register a procedure to be called on any nonfatal error

## SYNOPSIS

```
void VistaIOSetWarningHandler (VistaIOWarningHandler *handler)
```

**typedef void VistaIOWarningHandler (VistaIOStringConst** *message***);**

**void VistaIODefaultWarning (VistaIOStringConst** *message***);**

## ARGUMENTS

- *handler*

  **Specifies the new nonfatal error handler.**

- *message*

  **Specifies a null-terminated error message string to be reported.**

## DESCRIPTION

**VistaIOSetWarningHandler registers a procedure,** *handler***, as the** **nonfatal error handler. That procedure is called by [VistaIOWarning(3)](/VistaIOWarning/3.md) or** **by VistaIOSystemWarning(3) to report any nonfatal error. When called it** **is passed a string,** *message***, containing a textual description of the** **error.**

**Only one procedure serves as the nonfatal error handler at any one time.**

**Prior to the first call to VistaIOSetWarningHandler, the procedure** **VistaIODefaultWarning is the nonfatal error handler. This procedure will** **write the error message to the standard error stream, then return.** **VistaIODefaultWarning can be re-established as the fatal error handler at** **any time by calling VistaIOSetWarningHandler with a** **NULL** **argument.**

## EXAMPLES

**To adopt a warning handler that writes messages both to the standard error** **stream and to a log file, one might do the following:**

```
FILE *log_file;
void MyWarningHandler (message)
	VistaIOStringConst message;
{
	fputs (message, stderr);
	fputs (message, log_file);
}
int main (...)
{
	...
	log_file = fopen ("log", "w");
	VistaIOSetWarningHandler (MyWarningHandler);
	...
}
```

## SEE ALSO

[**VistaIOWarning**(3)](/VistaIOWarning/3.md), [**VistaIOSetErrorHandler**(3)](/VistaIOSetErrorHandler/3.md),

## AUTHOR

**Art Pope \<pope@cs.ubc.ca\>**

**Adaption to vistaio: Gert Wollny \<gw.fossdev@gmail.com\>**