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To print an array’s length, use the syntax for its programming language: JavaScript and Java use array.length, while C++17 provides std::size(array) for built-in arrays and supported containers. For example, in JavaScript:
const items = ["a", "b", "c"];
console.log(items.length); // 3Print an array’s length in JavaScript
JavaScript arrays have a length property, not a length() method. Read the property and pass it to console.log:
const colors = ["red", "green", "blue"];
console.log(colors.length); // 3The value reflects the highest array index plus one, not necessarily the number of populated slots. For instance, assigning a value at index 100 gives the array a length of 101 even if the earlier positions are empty. See MDN’s Array.length reference.
The property is writable, so changing it also changes the array: reducing the length deletes elements beyond the new endpoint; increasing it adds empty slots. Invalid lengths, such as a negative number, cause a RangeError. Details are in MDN’s Array.length reference.
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Print an array’s length in Java
Java arrays expose a final instance variable named length. Print it with an output statement such as System.out.println:
int[] values = {4, 8, 12};
System.out.println(values.length); // 3The length is fixed when the array is created. If you need a different size, create another array or use a collection type designed to grow. The Java Language Specification defines an array of length n as having components indexed from 0 through n - 1; an array may also be empty. See Java Language Specification, Chapter 10 and Section 10.2, Array Variables.
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Print an array’s length in C++17
In C++17, use std::size for a built-in array or a supported container. Include <iterator> and print the returned element count:
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#include <iterator>
int values[] = {4, 8, 12};
std::cout << std::size(values); // 3std::size returns a container’s size() or the extent of a built-in array. It counts elements, whereas sizeof reports storage in bytes. Applying sizeof to a pointer does not reveal the original array’s element count. See the C++ reference for std::size.
Which syntax should you use?
| Language | How to print the count | What it reports | Can the array length change? |
|---|---|---|---|
| JavaScript | console.log(array.length) |
Highest array index plus one; sparse slots count toward the length. | Yes. Changing length truncates the array or creates empty slots. |
| Java | System.out.println(array.length) |
The array’s number of components. | No. The length is fixed when the array is created. |
| C++17 | std::cout << std::size(array) |
Element count for a built-in array or supported container. | Depends on the array or container type. |
These examples cover JavaScript, Java, and C++17. The syntax differs across languages, so do not assume that .length or std::size applies to a language not covered here.
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