Tcl_Panic(3tcl)

💖 Tcl_Panic — report fatal error and abort 💖

okay bestie, pull up a chair because this is the "everything is on fire" page of the Tcl manual, and honestly? it's kind of iconic. this is from the Tcl Library Procedures collection, so grab your C compiler and your emotional support iced coffee 🫶

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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, bestie. it's giving template for the chaos.
• arg (in) — the arguments that match up with the format string. they gotta correspond, no cap.
• Tcl_PanicProc *panicProc (in) — the procedure that reports the fatal error message and then aborts. the designated panic-yell person 💅

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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 straight-up does not match their documentation — it calls Tcl_Panic to display a message describing the error and abort the process. not me being dramatic, that's literally the function's whole job 😭

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 get this — those same formatting rules are also used by the built-in Tcl command format. consistency queen 👑

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, bestie, it already left the group chat 💀

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. very "we tried to be helpful, here's a popup" of it ✨

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. slay, no extra work 🎀

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.

⚠️ okay important, listen up: 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. do not poke the bear, the bear is having a moment 🙈

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 for your records 🧚

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 energy, custom panic handler edition 💅

Tcl_SetPanicProc can not be used in stub-enabled extensions. that's just the rules, periodt.

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. it's public, it's for the people, it ate 🔥

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🌈 SEE ALSO 🌈

abort(3), printf(3), exec(3tcl), format(3tcl)

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👑 KEYWORDS 👑

abort, fatal, error

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and that's the whole page, bestie! this little gem is from Tcl 8.4, filed under Tcl_Panic(3tcl). go forth and panic responsibly 💜✨