PHP 函数 strlen() 的算法复杂度

Question

Recently I was asked this question on interview and I didn't know how to answer it.

Can anyone answer this question and describe it?

Answer 1

O(1) since the length is stored as an attribute: source

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Answer 2

我假设该函数是 O(n)，因为它需要遍历字符串一次。

Answer 3

php 7 source code see here

O(1) access attribute ZSTR_LEN(s) see here