TIP #183 Version 1.1: Add a Binary Flag to [open]

This is not necessarily the current version of this TIP.

Abstract

To handle binary files, one currently has to open the file, and then in a second step fconfigure it with -translation binary. This TIP proposes to add a flag "b" to open's access-argument to set initial translation to binary (rather than auto).

Rationale

ANSI-C fopen() supports an additional flag "b" in the mode- parameter especially for non-POSIX platforms, where it makes sure that no conversion takes place at reading or writing. The manual page for open mentions that [fconfigure] should be used as a substitute for the missing "b"-flag but I don't see anything wrong with a "b" flag as a possible shortcut for this [fconfigure]-call, so this TIP proposes that the access argument to open should support b as an additional letter (anywhere within the argument when used in the first form documented on the manual page) which will cause the initial configuration of the channel to be suitable for reading and/or writing binary data.

Thus, for an expectedly very little implementation effort, we can simplify:

  set fd [open $fname "w"]; fconfigure $fd -translation binary

to:

  set fd [open $fname "wb"]

which looks much more concise for such a common task.

This extra flag would only affect the initial translation state.

Enhancement

Tcl's [open] also tries to adopt the POSIX open() parameters (i.e. the second form documented for the access parameter on the manual page.) POSIX's open() doesn't know about binary or non-binary files, but Tcl does, so a new keyword "BINARY" could be introduced to offer this feature also to those who prefer list-of-flags syntax.

Copyright

This document has been placed in the public domain.

This is not necessarily the current version of this TIP.