PhpWarning: strstr () [function. strstr]: Emptydelimiter

Warning: strstr () [functionstrstr]: Emptydelimiter. it's very strange. Is there a problem with a certain parameter in the strstr function of php?

Warning: strstr () [function. strstr]: Empty delimiter. it's very strange. Is there a problem with a certain parameter in the strstr function of php ?, So I wrote a test example:

2. $ Text = "asdfghjklqwertyuiopzxcvbnm ";
3. // $ Key = "g ";
4. // According to the php error prompt Empty delimiter, it is determined that the value of $ text should not have a problem, so the key value is intentionally commented
5. If (strstr ($ text, $ key )){
6. Echo "found it ";
7. } Else {
8. Echo "not found ";
9. }
10. ?>

Strstr () does not report an error, so it is thought that the $ key value may be an empty string "". let's just try it. when strstr ($ text, "") is displayed, an error Warning is prompted: strstr () [function. strstr]: Empty delimiter