CFGETISPEED(3POSIX)

📦 version 2017a, in debian bookworm, debian trixie, ubuntu jammy, ubuntu noble, ubuntu resolute, ubuntu stonking

💖 CFGETISPEED(3POSIX) 💖

okay bestie, welcome to cfgetispeed — this is from the POSIX Programmer's Manual, volume 3POSIX, and it is literally the vibe check for your terminal's input speed. 🦋

🌸 PROLOG 🌸

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (so pls consult the corresponding Linux manual page for the details of Linux behavior, iykyk), or the interface may not be implemented on Linux at all. 🙈

✨ NAME ✨

cfgetispeed — get input baud rate. that's it, that's the whole job. 💅

🎀 SYNOPSIS 🎀

#include <termios.h>

speed_t cfgetispeed(const struct termios *termios_p);

👑 DESCRIPTION 👑

The cfgetispeed() function shall extract the input baud rate from the termios structure that the termios_p argument points to. 🫶

And this is the important part, no cap: this function shall return exactly the value in the termios data structure, without interpretation. it does not think about it. it does not editorialize. it does not manifest. it just hands you the raw number. periodt. ⭐

🌈 RETURN VALUE 🌈

Upon successful completion, cfgetispeed() shall return a value of type speed_t representing the input baud rate. iconic behavior honestly. 💜

💀 ERRORS 💀

No errors are defined.

not me having zero failure modes. the following sections are informative, bestie — meaning they're the lore, not the law. 📖

🍓 EXAMPLES 🍓

None.

🧚 APPLICATION USAGE 🧚

None.

🔥 RATIONALE 🔥

okay so, the tea: the term baud'' is used historically here, but it is **not technically correct**. This is properly bits per second'', which may not be the same as baud. However, the term is used because of the historical usage and understanding. so we all just keep saying baud like it's a group chat nickname that stuck. 😭

The cfgetospeed(), cfgetispeed(), cfsetospeed(), and cfsetispeed() functions do not take arguments as numbers — they take them as symbolic names. There are two reasons for this:

  1. Historically, numbers were not used because of the way the rate was stored in the data structure. This is retained even though a function is now used.
  2. More importantly, only a limited set of possible rates is at all portable, and this constrains the application to that set. (portability slay, tbh ✨)

There is nothing to prevent an implementation from accepting as an extension a number (such as 126), and since the encoding of the Bxxx symbols is not specified, this can be done to avoid introducing ambiguity.

Setting the input baud rate to zero was a mechanism to allow for split baud rates. Clarifications in this volume of POSIX.1‐2017 have made it possible to determine whether split rates are supported and to support them without having to treat zero as a special case. Since this functionality is also confusing, it has been declared obsolescent. 🚨

The 0 argument referred to is the literal constant 0, not the symbolic constant B0. This volume of POSIX.1‐2017 does not preclude B0 from being defined as the value 0; in fact, implementations would likely benefit from the two being equivalent.

This volume of POSIX.1‐2017 does not fully specify whether the previous cfsetispeed() value is retained after a tcgetattr() as the actual value or as zero. Therefore, conforming applications should always set both the input speed and output speed when setting either. do not skip one, bestie, i am begging. 🙏

In historical implementations, the baud rate information is traditionally kept in c_cflag. Applications should be written to presume that this might be the case (and thus not blindly copy c_cflag), but not to rely on it in case it is in some other field of the structure. Setting the c_cflag field absolutely after setting a baud rate is a non-portable action because of this. In general, the unused parts of the flag fields might be used by the implementation and should not be blindly copied from the descriptions of one terminal device to another. like... stop copy-pasting flags between devices, it's giving chaos. 💀

🦋 FUTURE DIRECTIONS 🦋

None.

🌸 SEE ALSO 🌸

  • cfgetospeed()
  • cfsetispeed()
  • cfsetospeed()
  • tcgetattr()

The Base Definitions volume of POSIX.1‐2017, Chapter 11, General Terminal Interface, <termios.h>

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

and that's the whole page, bestie!! 🎀 this one came to you from IEEE/The Open Group, 2017, and honestly? they ate. go forth and read your input baud rate exactly as it is, no interpretation, no drama. mwah. 💖✨👑

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