问题
var_dump("555555555555555555555" == "555555555555555555553"); //bool(true)
var_dump("aaaaaaaaaaaaaaaaaaaaa" == "aaaaaaaaaaaaaaaaaaaab"); //bool(false)
Why does this happen?
I know I can use
var_dump(strcmp("555555555555555555555", "555555555555555555553") == 0); //bool(false)
But why the first row returns true?
回答1:
It's a side effect of type-coercing. There's an article on phpsadness about it. Basically, the strings in the comparison are converted to numeric types, and due to precision loss, appear to be equal.
回答2:
In your first row
var_dump("555555555555555555555" == "555555555555555555553");
it is true
Why because, the type-coercing comparison operators will coerce both operands to floats if they both look like numbers, even if they are both already strings
This bug is discussed here
来源：https://stackoverflow.com/questions/19161722/php-long-numbers-in-string-comparison