PHP String Parsing Searching a substring with strpos
Example
strpos can be understood as the number of bytes in the haystack before the first occurrence of the needle.
var_dump(strpos("haystack", "hay")); // int(0)
var_dump(strpos("haystack", "stack")); // int(3)
var_dump(strpos("haystack", "stackoverflow"); // bool(false)
Checking if a substring exists
Be careful with checking against TRUE or FALSE because if a index of 0 is returned an if statement will see this as FALSE.
$pos = strpos("abcd", "a"); // $pos = 0;
$pos2 = strpos("abcd", "e"); // $pos2 = FALSE;
// Bad example of checking if a needle is found.
if($pos) { // 0 does not match with TRUE.
echo "1. I found your string\n";
}
else {
echo "1. I did not found your string\n";
}
// Working example of checking if needle is found.
if($pos !== FALSE) {
echo "2. I found your string\n";
}
else {
echo "2. I did not found your string\n";
}
// Checking if a needle is not found
if($pos2 === FALSE) {
echo "3. I did not found your string\n";
}
else {
echo "3. I found your string\n";
}
Output of the whole example:
1. I did not found your string
2. I found your string
3. I did not found your string
Search starting from an offset
// With offset we can search ignoring anything before the offset
$needle = "Hello";
$haystack = "Hello world! Hello World";
$pos = strpos($haystack, $needle, 1); // $pos = 13, not 0
Get all occurrences of a substring
$haystack = "a baby, a cat, a donkey, a fish";
$needle = "a ";
$offsets = [];
// start searching from the beginning of the string
for($offset = 0;
// If our offset is beyond the range of the
// string, don't search anymore.
// If this condition is not set, a warning will
// be triggered if $haystack ends with $needle
// and $needle is only one byte long.
$offset < strlen($haystack); ){
$pos = strpos($haystack, $needle, $offset);
// we don't have anymore substrings
if($pos === false) break;
$offsets[] = $pos;
// You may want to add strlen($needle) instead,
// depending on whether you want to count "aaa"
// as 1 or 2 "aa"s.
$offset = $pos + 1;
}
echo json_encode($offsets); // [0,8,15,25]
