CODEWITHSUNDEEP
c++
Anycorn
Anycorn

Reputation: 51555

C++, ternary operator operand evaluation rules

Lets say i have following code:

std::vector<T> R;
if (condition) R = generate();
...
for (int i = 0; i < N; ++i) {
    const auto &r = (R.empty() ? generate() : R);
}

It appears that generate is called regardless of R.empty(). Is that standard behavior?

Upvotes: 16

Views: 5794

Answers (1)

Andy Prowl
Andy Prowl

Reputation: 126542

From Paragraph 5.16/1 of the C++ 11 Standard:

Conditional expressions group right-to-left. The first expression is contextually converted to bool (Clause 4). It is evaluated and if it is true, the result of the conditional expression is the value of the second expression, otherwise that of the third expression. Only one of the second and third expressions is evaluated. Every value computation and side effect associated with the first expression is sequenced before every value computation and side effect associated with the second or third expression.

Upvotes: 27

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