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Logical XOR operator

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5 Sep 2002 185.9K   18   31
A simple implementation of a logical xor operator.

Introduction

Occasionally I come to a need of a logical xor operator (^^) that, obviously, doesn't exist in C++. However, it can be rather easily implemented.

Code listing

#define log_xor || log_xor_helper() ||


struct log_xor_helper {
    bool value;
};

template<typename LEFT>
log_xor_helper &operator ||(const LEFT &left, log_xor_helper &xor) {
    xor.value = (bool)left;
    return xor;
}

template<typename RIGHT>
bool operator ||(const log_xor_helper &xor, const RIGHT &right) {
    return xor.value ^ (bool)right;
}

Examples

0 log_xor 0 == false
0 log_xor 5 == true
8 log_xor 0 == true
8 log_xor 5 == false

Other details

  • Although they don't have to have the same type, operands should be castable into a simple boolean.
  • Precedence of log_xor operator is the same as logical or's (||) one.
  • If you decide to use it, I suggest you to add log_xor keyword to the usertype.dat file and insert somewhere the #pragma warning(disable: 4800) line.

License

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Comments and Discussions

 
GeneralToo bad... Pin
UltraJoe9-Sep-02 8:42
UltraJoe9-Sep-02 8:42 
QuestionWhat is this all about? Pin
Anonymous6-Sep-02 16:43
Anonymous6-Sep-02 16:43 
AnswerRe: What is this all about? Pin
Goran Mitrovic7-Sep-02 3:01
Goran Mitrovic7-Sep-02 3:01 
GeneralRe: What is this all about? Pin
Roman Nurik7-Sep-02 6:04
Roman Nurik7-Sep-02 6:04 
GeneralRe: What is this all about? Pin
Goran Mitrovic7-Sep-02 6:24
Goran Mitrovic7-Sep-02 6:24 
GeneralRe: What is this all about? Pin
Goran Mitrovic7-Sep-02 6:39
Goran Mitrovic7-Sep-02 6:39 
GeneralRe: What is this all about? Pin
Tim Smith9-Sep-02 8:53
Tim Smith9-Sep-02 8:53 
GeneralRe: What is this all about? Pin
Goran Mitrovic9-Sep-02 10:42
Goran Mitrovic9-Sep-02 10:42 
Using stack space for storing variables isn't that bad since they will rarely be actually written in real memory (cache is able to delay writes for quite a while).

Templates could lead to bad optimisations, but, in my opinion, that's not really a thing a developer should think too much about - algorithms are the ones that count.

Two things:
- I know that VC6 had some problems with deeply inlined functions, but, I have a reason to believe (haven't really checked) they extended them (those limits are probably simple constants) because the processors are much faster today, so, proper optimisations won't take that long and, there is a 'whole program optimisation' feature that would be meaningless if limits were set quite low.
- Compiler can always be changed. For example, it is known that KAI based compilers (Intel C++ now) have unlimited level of function analysis.



- Goran.

GeneralCool Beans Pin
Anonymous6-Sep-02 9:46
Anonymous6-Sep-02 9:46 
GeneralRe: Cool Beans Pin
Goran Mitrovic6-Sep-02 14:35
Goran Mitrovic6-Sep-02 14:35 
GeneralNice :-) Pin
Nish Nishant6-Sep-02 6:33
sitebuilderNish Nishant6-Sep-02 6:33 

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