Matlab中能否创建未初始化元素且未指定长度的一维数组？

Great question! Let's break this down clearly for MATLAB:

First, let's get straight to the core point: Strictly speaking, you cannot create a 1D array in MATLAB that has neither initialized elements nor a defined length. MATLAB is an array-centric language, and every array must have explicit dimension properties (even if those dimensions are zero). That said, there are workarounds that let you achieve the behavior of starting with an "empty, unspecified-length" array and populating it later.

1. Use an empty array (length 0) #

The closest thing to an "uninitialized, unspecified-length" array is a 1x0 empty array. It has a defined length (0) but no elements, and you can dynamically add elements to it later:

% Create a 1D empty array
my_arr = [];

% Check its dimensions (returns [1 0], confirming it's a 1x0 array)
size(my_arr)

% Dynamically add elements one by one
my_arr(end+1) = 42;
my_arr(end+1) = 123;

% Now my_arr is [42, 123]

2. Implicit dynamic creation #

If you skip initializing the array entirely and directly assign to the end+1 index, MATLAB will automatically create an array for you, starting with length 1 and expanding as needed:

% No prior array definition—just assign to end+1
dynamic_arr(end+1) = 7;

% MATLAB creates a 1x1 array [7] automatically
dynamic_arr(end+1) = 14;
dynamic_arr(end+1) = 21;

% Now dynamic_arr is [7, 14, 21]

A quick performance note #

While dynamic expansion is convenient, it’s not ideal for large datasets. Every time you add an element, MATLAB has to reallocate memory for the larger array, which can slow down your code. If you have a rough idea of how many elements you’ll need later, preallocate the array upfront (e.g., prealloc_arr = zeros(1, 100);) to avoid this overhead.

Summary #

You can’t create a 1D array in MATLAB with no length and no initialized elements—all arrays require defined dimensions. But using an empty array (1x0) or relying on implicit dynamic creation lets you mimic the workflow of starting with an "unspecified" array and building it out over time.

内容的提问来源于stack exchange，提问作者Fitzgerald Brooks