This is a text-only version of the following page on https://raymii.org:
---
Title : and & or are valid in C++ (alternative tokens)
Author : Remy van Elst
Date : 16-12-2019
URL : https://raymii.org/s/blog/and_or_are_valid_Cpp.html
Format : Markdown/HTML
---
[A post][3] on [lobste.rs][1] on the C feature trigraphs triggered me to write
this piece on the C++ feature, alternative tokens. I've recently suprised a co-
worker by using an if statement with 'or' instead of '||', which works fine, but
he never saw it before. It's in C++ since C++ 11, but MSVC requires a specific
compiler flag ('/Za') or the "iso646.h" header. This post has a few samples on
the usage inclusing other alternative tokens like bitor, xor and or_eq.
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The `or` and `and` feel more natural to me. Even though I perfectly know and
understand the `||` and `&&` operators, I would prefer the alternative tokens
when reading code. For bitsets, the `bitand`, `compl` and `bitor` also read
better, in my opinion. The trigraph feature of C was removed in C++ 17. Those
are weird.
### Alternative tokens
The motivation for the alternative tokens can be found [on cppreference][4]:
C++ (and C) source code may be written in any non-ASCII 7-bit character set that
includes the [ISO 646:1983][11] invariant character set. However, several C++
operators and punctuators require characters that are outside of the ISO 646
codeset: `{, }, [, ], #, , ^, |, ~`. To be able to use character encodings where
some or all of these symbols do not exist (such as the German [DIN 66003][12]),
C++ defines the following alternatives composed of ISO 646 compatible
characters.
There are alternative spellings for several operators and other tokens that use
non-ISO646 characters. In all respects of the language, each alternative token
behaves exactly the same as its primary token, except for its spelling (the
stringification operator can make the spelling visible). The two-letter
alternative tokens are sometimes called "digraphs"
The characters `&` and `!` are invariant under ISO-646, but alternatives are
provided for the tokens that use these characters anyway to accomodate even more
restrictive historical charsets.
There is no alternative spelling (such as `eq`) for the equality operator `==`
because the character `=` was present in all supported charsets.
### Some examples
An few examples on the use of alternative tokens, starting with `and` and `or`.
bool ex1 { false };
bool ex2 { true };
if ( ex1 or ex2) // instead of ||
{
std::cout << "Hello, World!" << std::endl;
}
Result:
Hello, World!
#### Example 2, not and
bool ex1 { false };
bool ex2 { true };
if (not ex1 and ex2) // instead of (!ex && ex2)
{
std::cout << "Hello, World!" << std::endl;
}
Result:
Hello, World!
#### Example 3, square brackets and curly braces
bool b<:2:> <%true, true%>; // instead of bool b[2] {true, true}
if (b<:1:>)
{
std::cout << "Hello, World!" << std::endl;
}
Result:
Hello, World!
#### Example 4, bitand
std::bitset<4> bs1 { 0011 };
std::bitset<4> bs2 { 0001 };
auto bs3 = bs1 bitand bs2; //instead of |
std::cout << bs3 << std::endl;
Result:
0001
### All tokens
The [full list][2] of alternative tokens:
Alternative Primary
<% {
%> }
<: [
:> ]
%: #
%:%: ##
and &&
bitor |
or ||
xor ^
compl ~
bitand &
and_eq &=
or_eq |=
xor_eq ^=
not !
not_eq !=
[1]: https://lobste.rs/s/zaiaip/c_what_fuck#c_hmvlv3
[2]: https://en.cppreference.com/w/cpp/language/operator_alternative
[3]: https://bowero.nl/blog/2019/12/15/c-what-the-fuck/
[11]: https://en.wikipedia.org/wiki/ISO_646
[12]: http://de.wikipedia.org/wiki/DIN_66003
---
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