正则表达式匹配价格字符串

Question

I am new in PHP. I was trying to check if one of the form inputs (contained in $price for this example) is a decimal as follows:

if(!preg_match("\\d+(.\\d{1,2})?", $price))
    //do something

In Java, it would have been

price.matches("\\d+(.\\d{1,2})?")

But the same regex is not working in PHP. Does preg_match match substrings as well?

I expect the following inputs to be true:

300
300.5
300.56

All other formats should be false. I cannot figure out how to do that in PHP.

Answer 1

Let's do this right:

is_string($price) and trim($price); // Might be worth doing first
if(preg_match('~^\\d+(?:\\.\\d{1,2})?$~', $price)) {
   $price = floatval($price); // Kewl, keep going
}else{
   // Unkewl, fail
}

1. Wrap RegExp in ~ character. Any non-reserved character works as a wrapper and / is terrible when dealing with URLs or HTML as you need to escape it too. It's a nightmare.
2. Force the string to exact match by enclosing in ^ and $ and not a contain match like all these variants here.
3. Wrap string in single quotes if you don't have PHP "{$variables}" that need to be expanded in them.
4. Escape \ even in single quoted string like this \d or \.!
5. Don't capture the block, it does not matter anyway but is a performance thing.

:) Rant done!