在逗号分隔的前缀列表中查找前缀的有效方法

Question

I have a prefix stored in a variable

$prefix = “07”;

And coma separated list of prefixes stored in another variable (the list is provide by user using text box)

$allPrefixes = “07,03,+17”;

What is efficient way to check if the value stored in $prefix is one of the prefixes stored in $allPrefixes

Answer 1

I'd go for a regex to match:

$regex = "/(^|,)".$prefixe."(,|$)/";
preg_match($regex,$allPrefixes);

• On beginning of string before a comma,
• between commas or
• after comma, at end of string

The above regex will match, for example, 07 but not 007.

General knowledge, not applicable in this case:
If 007 is not likely to appear, or prefixe is not likely to be a substring of any other prefixe, then you can use strpos($allPrefixes, $prefixe) > -1 instead, which is quite more efficient.

However
wrapping the $allPrefixes string between , and using strpos might be both efficient and accurate:

strpos(",".$allPrefixes.",", ",".$prefixe.",")

will match 07 but not 007