Substring ExamplesGet parts of strings with the substr function, and modify chars within strings by assigning them.
This page was last reviewed on May 18, 2023.
Substring. In PHP programs we often need to access just a part of a string, not the entire string. Consider the word "substring": we can just access the "string" part of it.
Function arguments. The PHP substr function receives the source string, the offset index (0-based) and a length. We must pass a length, not the end index.
Substr example. To begin, we invoke the substr function twice. We first declare a string containing the letters "carrot" and then we get parts of it.
Part 1 We take the first 3 characters of "carrot" and place them in a new string. The result is printed with var_dump.
Part 2 We pass a negative argument to substring to get characters from the end of the string.
$word = "carrot"; // Part 1: get first 3 characters. $result1 = substr($word, 0, 3); var_dump($result1); // Part 2: get last 3 characters. $result2 = substr($word, -3); var_dump($result2);
string(3) "car" string(3) "rot"
Assign index. We can modify a string in PHP by assigning into it. When we assign a character by index, we can only place one new character there.
Part 1 We access character at index 1. Since strings are 0-based, this is the "b" in "abc."
Part 2 We modify the string by assigning into it. The second character "b" is replaced with a question mark.
Warning If you try to insert more than 1 character by assigning an index, the second and later characters are lost.
// Part 1: get character from string. $input = "abc"; $second = $input[1]; var_dump($second); // Part 2: change character in string. $input[1] = "?"; var_dump($input);
string(1) "b" string(3) "a?c"
Substr replace. This method changes a range of characters in the input string. So we specify a start index, and a length, and that part of the string is replaced with something else.
// The input string. $input = "abc abc"; // Replace chars starting at index 1 and continuing for 2 chars. $result = substr_replace($input, "??", 1, 2); var_dump($result);
string(7) "a?? abc"
Taking substrings in PHP is common—nearly every PHP program in the real world does this. For 1-character substrings, we can use an index expression.
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Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on May 18, 2023 (edit).
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