C++ operator precedence Logical && and || operators: short-circuit
Example
&& has precedence over ||, this means that parentheses are placed to evaluate what would be evaluated together.
c++ uses short-circuit evaluation in && and || to not do unnecessary executions.
If the left hand side of || returns true the right hand side does not need to be evaluated anymore.
#include <iostream>
#include <string>
using namespace std;
bool True(string id){
cout << "True" << id << endl;
return true;
}
bool False(string id){
cout << "False" << id << endl;
return false;
}
int main(){
bool result;
//let's evaluate 3 booleans with || and && to illustrate operator precedence
//precedence does not mean that && will be evaluated first but rather where
//parentheses would be added
//example 1
result =
False("A") || False("B") && False("C");
// eq. False("A") || (False("B") && False("C"))
//FalseA
//FalseB
//"Short-circuit evaluation skip of C"
//A is false so we have to evaluate the right of ||,
//B being false we do not have to evaluate C to know that the result is false
result =
True("A") || False("B") && False("C");
// eq. True("A") || (False("B") && False("C"))
cout << result << " :=====================" << endl;
//TrueA
//"Short-circuit evaluation skip of B"
//"Short-circuit evaluation skip of C"
//A is true so we do not have to evaluate
// the right of || to know that the result is true
//If || had precedence over && the equivalent evaluation would be:
// (True("A") || False("B")) && False("C")
//What would print
//TrueA
//"Short-circuit evaluation skip of B"
//FalseC
//Because the parentheses are placed differently
//the parts that get evaluated are differently
//which makes that the end result in this case would be False because C is false
}
