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C extension: <? and >? operators

Take a look at the top answer (by sclo) to problem D of this Google Code Jam. It's C++ code, it must have compiled, and it contains statements such as this one:

double& ret = F[mask][cur][b];
if(j==cur) {
  ret<?=f(tmp,j,b||bad[i])+M[cur][i];   // WTF is <?=   ???
}

This doesn't compile in my Visual Studio 2008. What does the <?= mean?

Could it be C++0x code?! If it is, then it can't be compiled in VS2008. — Rafid, Jan 19 '11 at 10:57
I don't know, the file extensions is CPP. I've lost touch with the C++ language a few years ago. — ripper234, Jan 19 '11 at 11:01
My first hunch was that it would be a [digraph or trigraph](http://en.wikipedia.org/wiki/Digraphs_and_trigraphs), however it doesn't look like any of the known sequences. — Péter Török, Jan 19 '11 at 11:05

score 19 · Accepted Answer · edited May 23 '17 at 12:26

19

It's a gcc extension: C extension: <? and >? operators

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...

edited May 23 '17 at 12:26

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answered Jan 19 '11 at 11:05

Luca Matteis

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+1: Removed from GCC around version 4 (from the answer on linked page). – xk0der Jan 19 '11 at 11:13

score 3 · Answer 2 · answered Jan 19 '11 at 11:05

3

It's simply not valid C++. < Might be less than, an open angle bracket for a template argument list, or the start of a digraph however non of those can be followed by ?, then =.

answered Jan 19 '11 at 11:05

CB Bailey

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score 3 · Answer 3 · answered Jan 19 '11 at 11:36

It's a now deprecated g++ extension to the c++ language.

a <? b is the minimum, returning the smaller of the numeric values a and b;

a >? b is the maximum, returning the larger of the numeric values a and b.

There are also compound versions

<?=

and

>?=

that do assignment as well.

score 0 · Answer 4 · answered Jan 19 '11 at 11:04

0

It doesn't compile also with GCC, and I've never heard of an operator <?=.

Anyway I would hazard a guess that a<?=b could have a semantics like: a = (a<b) ? b : a, but again, this is just a guess.

answered Jan 19 '11 at 11:04

peoro

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