Tcl_SetErrno(3tcl)

💖 Tcl_SetErrno — bestie edition 💖

okay so this is a page from the Tcl Library Procedures manual, and it's literally about Tcl_SetErrno, Tcl_GetErrno, Tcl_ErrnoId, Tcl_ErrnoMsg, and Tcl_WinConvertError — the whole squad that manipulates errno so you can store and retrieve error codes. no cap. 🫶

---

✨ NAME ✨

Tcl_SetErrno, Tcl_GetErrno, Tcl_ErrnoId, Tcl_ErrnoMsg, Tcl_WinConvertError — manipulate errno to store and retrieve error codes 💅

---

🌸 SYNOPSIS 🌸

#include <tcl.h>

void
Tcl_SetErrno(errorCode)

int
Tcl_GetErrno()

const char *
Tcl_ErrnoId()

const char *
Tcl_ErrnoMsg(errorCode)

void
Tcl_WinConvertError(winErrorCode)

---

🎀 ARGUMENTS 🎀

• int errorCode (in) — a POSIX error code, like ENOENT. yes bestie, that kind of thing 💖
• DWORD winErrorCode (in) — a Windows or Winsock error code, like ERROR_FILE_NOT_FOUND. very Windows-coded of it 🪟

---

👑 DESCRIPTION 👑

so Tcl_SetErrno and Tcl_GetErrno are your portable hookup to the errno variable — that's the thing that records a POSIX error code after system calls and other operations, such as Tcl_Gets. and why do these procedures even need to exist, you ask? because global variable accesses literally cannot be made across module boundaries on some platforms. it's giving necessary, fr fr. 😭

Tcl_SetErrno sets the errno variable to the value of the errorCode argument. so if you're writing C procedures that wanna hand error info back to their callers via errno, call Tcl_SetErrno instead of setting errno directly. do not go rogue. 💅

Tcl_GetErrno returns the current value of errno. any procedure wishing to access errno should call this procedure instead of accessing errno directly. same energy, but the correct way 🫶

Tcl_ErrnoId and Tcl_ErrnoMsg return string representations of errno values:

• Tcl_ErrnoId returns a machine-readable textual identifier, such as "EACCES", that corresponds to the current value of errno. 🤖
• Tcl_ErrnoMsg returns a human-readable string, such as "permission denied", that corresponds to the value of its errorCode argument. and that errorCode argument is typically the value returned by Tcl_GetErrno. cute lil pipeline, honestly ✨

⚠️ okay important: the strings returned by these functions are statically allocated, so the caller must not free or modify them. not even a little. don't touch. it's giving hands off 🔥

Tcl_WinConvertError (Windows only, bestie) maps the passed Windows or Winsock error code to a POSIX error and stores it in errno. very translator era of it 💜

---

🔑 KEYWORDS 🔑

errno, error code, global variables

---

and that's the whole page!! this one's from the Tcl 8.3 era, dated back in the Tcl_SetErrno(3tcl) era of the world, sitting in the Tcl Library Procedures manual 💖 thanks for reading bestie, go forth and never set errno directly again 🎀✨🦋