Tcl_Panic(3)

💀 Tcl_Panic — report fatal error and abort 💀

ok so bestie, we're in Tcl Library Procedures territory and this one is genuinely the "everything is on fire" page 🔥 like no cap, this is the last resort function. buckle up 🎀

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✨ SYNOPSIS ✨

#include <tcl.h>

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

void
Tcl_PanicVA(format, argList)

void
Tcl_SetPanicProc(panicProc)

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🌸 ARGUMENTS 🌸

• const char* format (in) — a printf-style format string, the blueprint for the message 💅
• arg (in) — the arguments that match up with the format string, one per placeholder fr fr
• va_list argList (in) — an argument list of arguments matching the format string. it must have been initialized using va_start, and cleared using va_end — do not skip that, bestie, that's the whole vibe check 😭
• Tcl_PanicProc *panicProc (in) — the procedure that reports the fatal error message and aborts

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🦋 DESCRIPTION 🦋

so here's the tea ☕ 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. that's it, that's the whole job, main character energy of "we are done here" 👑

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. and the same formatting rules are also used by the built-in Tcl command format — so if you know one, you know the other, iykyk ✨

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 — like, ever, it's not coming back, that's the whole point 💀 On Windows, when a debugger is running, the formatted error message is sent to the debugger instead. and 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. cute lil popup of doom 🫶

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. but listen — 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. like bestie, the house is on fire, please don't go rummaging through the drawers 🙈

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. slay, customizable doom 💅

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 you too can panic, iconically 🌈

Tcl_PanicVA is the same as Tcl_Panic except that instead of taking a variable number of arguments it takes an argument list. same energy, different packaging 🎁

⚠️ real talk: this function aborts your process. there is no return, there is no recovery, there is no "jk". if you're calling this, you already know 💀

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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 the whole page, bestie 🧚💖 this one comes straight from the Tcl crew, version 8.4, dated the day it shipped, and it's filed under Tcl_Panic(3) — go forth and panic responsibly 💜🍓