Why does “echo strcmp('60', '100');” in php output 5?

问题

PHP's documentation on this function is a bit sparse and I have read that this function compares ASCII values so...

echo strcmp('hello', 'hello');
//outputs 0 as expected - strings are equal.
echo '<hr />';

echo strcmp('Hello', 'hello');
//outputs -32, a negative number is expected as 
//uppercase H has a lower ASCII value than lowercase h.
echo '<hr />';

echo strcmp('60', '100');
//outputs 5.

The last example is confusing me. I don't understand why it is outputting a positive number.

• ASCII Value of 0 = 48
• ASCII Value of 1 = 49

• ASCII Value of 6 = 54

• Total ASCII value of '60' = (54 + 48) = 102

• Total ASCII value of '100' = (49 + 48 + 48) = 145

The strcmp() functions is saying that '60' is "greater" than '100' even though it seems that the ASCII value and string length of '100' is greater than '60'

Can anyone explain why?

Thanks

回答1:

strcmp() returns the difference of the first non-matching character between the strings.

6 - 1 is 5.

When you look at it, you are probably not seeing the characters or digits—just the numbers

回答2:

Because strcmp() stops at the first difference it finds. Hence the difference between the ASCII value of '1' and the ASCII value of '6'

回答3:

6 is 5 "larger" than 1. This is lexical comparison. The first character is different, that's where the comparison stops.

来源：https://stackoverflow.com/questions/9289571/why-does-echo-strcmp60-100-in-php-output-5