Tcl_Panic(3)

✨ Tcl_Panic — bestie, it's giving "we have to talk" 💀

okay so this is the manual page for the Tcl library's panic squad: Tcl_Panic, Tcl_SetPanicProc and Tcl_ConsolePanic. Their whole job? Report a fatal error and then abort. No cap. 🫶

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🌸 NAME 🌸

Tcl_Panic, Tcl_SetPanicProc, Tcl_ConsolePanic — report fatal error and abort 💅

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✨ SYNOPSIS ✨

#include <tcl.h>

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

const char *
Tcl_SetPanicProc(panicProc)

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

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🎀 ARGUMENTS 🎀

• const char* format (in) — a printf-style format string, literally the blueprint for the message.
• arg (in) — the arguments that match up with the format string. they gotta line up, bestie.
• Tcl_PanicProc *panicProc (in) — the procedure that reports the fatal error message and aborts. that's the whole gig.

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💖 DESCRIPTION 💖

So here's the tea: when the Tcl library clocks that its internal data structures are in an inconsistent state, or that its C procedures got called in a way that does not match their documentation, it calls Tcl_Panic to show a message describing the error and then abort the process. 💀

The format argument is a format string that describes how to format the rest of the arguments, arg, into an error message — following the exact same formatting rules as the printf family of functions. and guess what, the built-in Tcl command format uses those same rules too. consistency slay. ✨

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. and like… Tcl_Panic does not return. ever. periodt.

🪟 On Windows, when a debugger is running, the formatted error message goes to the debugger instead. And if the windows executable doesn't have a stderr channel (e.g. wish.exe), then a system dialog box pops up to display the panic message. iconic behaviour honestly.

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 that Tcl uses), you can call Tcl_SetPanicProc with Tcl_ConsolePanic as its argument. on platforms that only have one C runtime (which is almost all platforms except Windows), Tcl_ConsolePanic is equivalent to NULL. noted. 📝

Tcl_SetPanicProc can be used to modify the behaviour 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.

⚠️ okay this part matters: panicProc should avoid making calls into the Tcl library, or into other libraries that may call the Tcl library — because the original call to Tcl_Panic is basically saying the Tcl library is not in a state of reliable operation. do not poke the bear, bestie. 🙈

The result of Tcl_SetPanicProc is the full Tcl version with build information (e.g., 9.0.0+abcdef...abcdef.gcc-1002). cute little receipt. 🧾

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. main character customisation energy. 👑

Tcl_SetPanicProc can not be used in stub-enabled extensions. sorry bestie, that's the rule.

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. so like, you're invited to the party too. 🎉

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🦋 SEE ALSO 🦋

• abort(3)
• printf(3)
• exec(n)
• format(n)

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🌈 KEYWORDS 🌈

• abort
• fatal
• error

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and that's a wrap, bestie 💜 this lil page lives under the Tcl Library Procedures umbrella and the footer says it's from Tcl 8.4, dated on the Tcl_Panic(3) page itself. go forth and panic responsibly. 🎀✨