The terms substr
and substring
are commonly used in various programming languages to extract portions of a string. Although they may seem similar, there are important differences in their usage and behavior depending on the language.
1. substr
(Substring by position and length)
- General behavior:
substr
typically requires two arguments: the starting position and the length of the substring. - Starting position: The index of the first character to include in the result.
- Length: The number of characters to extract starting from the given position.
- In some languages,
substr
may support a third argument (negative length) to indicate that it should extract the substring up to the end.
Example in JavaScript:
let str = "Hello, world!";
let subStr = str.substr(7, 5); // Starts at position 7, extracts 5 characters
console.log(subStr); // Output: world
2. substring
(Substring by position range)
- General behavior:
substring
typically requires two arguments: the start index and the end index.- Start index: The position where the substring should begin.
- End index: The position where the substring should end (not inclusive).
- If the end index is greater than the string length,
substring
will return up to the end of the string. - The start index cannot be greater than the end index (if this happens, the two indices are swapped).
Example in JavaScript:
let str = "Hello, world!";
let subStr = str.substring(7, 12); // Extracts from position 7 to 12 (end index not included)
console.log(subStr); // Output: world
Key Differences:
Feature | substr |
substring |
---|---|---|
Arguments | Requires start position and length |
Requires start position and end position |
End behavior | Extracts a fixed length starting at a position | Extracts between start and end index (not inclusive of end) |
Negative indices | Supports negative indices to count from the end | Does not support negative indices |
Start > End | No swapping, may return an empty string or error | Swaps indices if the start is greater than the end |
Length parameter | Must specify the length of the substring | Does not use a length parameter, only start and end positions |
Example in JavaScript (further comparison):
let str = "Hello, world!";
// Using substr
let subStr1 = str.substr(7, 5); // Starts at 7, length 5 => "world"
let subStr2 = str.substr(-6, 5); // Starts 6 characters from the end, length 5 => "world"
// Using substring
let subStr3 = str.substring(7, 12); // Starts at 7, ends at 12 => "world"
let subStr4 = str.substring(12, 7); // Starts at 12, ends at 7 (will swap) => "world"