Tcl\_Panic(3) Tcl Library Procedures Tcl\_Panic(3)

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```

# [NAME](#NAME)

Tcl\_Panic, Tcl\_SetPanicProc, Tcl\_ConsolePanic - report fatal error and abort

# [SYNOPSIS](#SYNOPSIS)

```
#include <tcl.h>

Tcl_Panic(format, arg, arg, ...)

const char *
Tcl_SetPanicProc(panicProc)

Tcl_ConsolePanic(format, arg, arg, ...)
```

# [ARGUMENTS](#ARGUMENTS)

const char *\*format* (in)

A printf-style format string.

*arg* (in)

Arguments matching the format string.

Tcl\_PanicProc *\*panicProc* (in)

Procedure to report fatal error message and abort.

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```

# [DESCRIPTION](#DESCRIPTION)

When the Tcl library detects that its internal data structures are in an inconsistent state, or that its C procedures have been called in a manner inconsistent with their documentation, it calls **Tcl\_Panic** to display a message describing the error and abort the process. The *format* argument is a format string describing how to format the remaining arguments *arg* into an error message, according to the same formatting rules used by the **printf** family of functions. The same formatting rules are also used by the built-in Tcl command **format**.

In a freshly loaded Tcl library, **Tcl\_Panic** prints the formatted error message to the standard error file of the process, and then calls **abort** to terminate the process. **Tcl\_Panic** does not return. On Windows, when a debugger is running, the formatted error message is sent to the debugger instead. If the windows executable does not have a stderr channel (e.g. **wish.exe**), then a system dialog box is used to display the panic message.

If your application doesn't use **Tcl\_Main** or **Tk\_Main** and you want to implicitly use the stderr channel of your application's C runtime (instead of the stderr channel of the C runtime used by Tcl), you can call **Tcl\_SetPanicProc** with **Tcl\_ConsolePanic** as its argument. On platforms which only have one C runtime (almost all platforms except Windows) **Tcl\_ConsolePanic** is equivalent to NULL.

**Tcl\_SetPanicProc** may be used to modify the behavior of **Tcl\_Panic**. The *panicProc* argument should match the type **Tcl\_PanicProc**:

```
typedef void Tcl_PanicProc(


        const char *format,


        arg, arg,...);
```

After **Tcl\_SetPanicProc** returns, any future calls to **Tcl\_Panic** will call *panicProc*, passing along the *format* and *arg* arguments. *panicProc* should avoid making calls into the Tcl library, or into other libraries that may call the Tcl library, since the original call to **Tcl\_Panic** indicates the Tcl library is not in a state of reliable operation.

The result of **Tcl\_SetPanicProc** is the full Tcl version with build information (e.g., **9.0.0+abcdef...abcdef.gcc-1002**).

The typical use of **Tcl\_SetPanicProc** arranges for the error message to be displayed or reported in a manner more suitable for the application or the platform.

**Tcl\_SetPanicProc** can not be used in stub-enabled extensions.

Although the primary callers of **Tcl\_Panic** are the procedures of the Tcl library, **Tcl\_Panic** is a public function and may be called by any extension or application that wishes to abort the process and have a panic message displayed the same way that panic messages from Tcl will be displayed.

# [SEE ALSO](#SEE_ALSO)

[abort(3)](/man/os/tcl/abort.3), [printf(3)](/man/os/tcl/printf.3), [exec(n)](/man/os/tcl/exec.n), [format(n)](/man/os/tcl/format.n)

# [KEYWORDS](#KEYWORDS)

abort, fatal, error

8.4 Tcl

---

Document: Tcl_SetPanicProc(3) from tcl 9.1.0-r1 (Chainguard OS)
Source: https://downloads.sourceforge.net/project/tcl/Tcl/9.1.0/tcl9.1.0-src.tar.gz