C extension: ? operators

Question

I observed that there was at some point a <? and >? operator in GCC. How can I use these under GCC 4.5? Have they been removed, and if so, when?

Offset block_count = (cpfs->geo.block_size - block_offset) <? count;
cpfs.c:473: error: expected expression before ‘?’ token

*"Note that this question is specific to C."* -- Note that it is actually specific to G++... — DevSolar, May 12 '16 at 09:20

score 38 · Accepted Answer · edited May 06 '15 at 11:44

38

Recent manuals say:

The G++ minimum and maximum operators (‘<?’ and ‘>?’) and their compound forms (‘<?=’) and ‘>?=’) have been deprecated and are now removed from G++. Code using these operators should be modified to use std::min and std::max instead.

A quick search of the past documents seems to indicate that they were removed around version 4.0 (3.4.6 includes them, 4.0.4 does not).

edited May 06 '15 at 11:44

Barry

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answered Aug 09 '10 at 04:55

Carl Norum

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@Matt Joiner, That's what the docs say, yes: "GNU C++ (but not in GNU C)". – Carl Norum Aug 09 '10 at 14:01
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I'd like to give +1 if you can provide a link. – Matt Joiner Aug 09 '10 at 16:53
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@Matt Joiner, SRSLY? How about google? Here: http://gcc.gnu.org/onlinedocs/gcc-3.4.6/gcc/ – Carl Norum Aug 09 '10 at 16:54
Yeah... it's sad that it was removed. `a = b;` was a neat trick! Super concise and easy to read. Okay... `a = std::min(a, b);` is not that bad either. 8-) – Alexis Wilke Jan 30 '12 at 05:17
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That's not that sad, because one could spend looong time trying to understand what the hell this code is doing, if he hadn't known gnu extensions. – cubuspl42 Apr 26 '13 at 20:08
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@CarlNorum: One should be citing with a link in the first place. – Matt Joiner Feb 10 '14 at 08:22
@cubuspl42 and searching for code containing ``, `>?`, `=`, and/or `>?=` on Google might be hard because Google doesn't always play well with symbols. – RastaJedi May 12 '16 at 05:35
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@AlexisWilke but I must admit, it does look a cool neat trick and I would definitely use it for the same purpose as OP if it wasn't replaced/deprecated. – RastaJedi May 12 '16 at 05:56

paxdiablo · Answer 2 · 2016-05-12T09:16:33.287

Earlier iterations of g++ (not the C compiler) used these operators for giving you the minimum or maximum values but they've long been deprecated in favour of std::min and std::max.

Basically, they equated to (but without the possibility of double evaluation of a or b):

a <? b       -->       (a < b) ? a : b
a >? b       -->       (a > b) ? a : b

In terms of replacing them (and you really should replace them), you can use something like:

Offset block_count = cpfs->geo.block_size - block_offset;
if (block_count > count) block_count = count;

or equivalents using std::min.

I'm not a big fan of using C/C++ "extensions" (especially ones that have been deprecated and/or removed) since they tie me to a specific implementation of the language.

You should never use a non-standard extension where a perfectly adequate standard method is available.

C extension: ? operators

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