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Posted 5 Sep 2002


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Logical XOR operator

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3.10/5 (13 votes)
5 Sep 2002
A simple implementation of a logical xor operator.


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;


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.


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Comments and Discussions

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 
The problem is that there are limits. I don't know about this specific example, however, the more deeply nested your templates get, the more chance the optimizer is going to produce bad code. I have seen many cases with STL where doing loops the right way ended up with poor execution speed because of register exhaustion during the optimization phase. It isn't that the compiler really ran out of registers, it is just that it doesn't fully utilize the registers it has. This results in such problems as using stack space to store temporary values.

Like I said, I don't know about this specific case, but in my own work, I have backed off of using templates when other simpler solutions exist. They just don't work as well as we have been lead to believe.

Tim Smith

"Programmers are always surrounded by complexity; we can not avoid it... If our basic tool, the language in which we design and code our programs, is also complicated, the language itself becomes part of the problem rather that part of the solution."
Hoare - 1980 ACM Turing Award Lecture
GeneralRe: What is this all about? Pin
Goran Mitrovic9-Sep-02 10:42
Goran Mitrovic9-Sep-02 10:42 
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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