Command Syntax and Function Syntax

In MATLAB, these statements are equivalent:

load durer.mat % Command syntax load('durer.mat') % Function syntax

This equivalence is sometimes referred to ascommand-function duality.

All functions support this standard function syntax:

[output1, ..., outputM] = functionName(input1, ..., inputN)

In function syntax, inputs can be data, variables, and even MATLAB expressions. If an input is data, such as the numeric value2or the string array["a" "b" "c"], MATLAB passes it to the function as-is. If an input is a variable MATLAB will pass the value assigned to it. If an input is an expression, like2+2orsin(2*pi), MATLAB evaluates it first, and passes the result to the function. If the functions has outputs, you can assign them to variables as shown in the example syntax above.

Command syntax is simpler but more limited. To use it, separate inputs with spaces rather than commas, and do not enclose them in parentheses.

functionName input1 ... inputN

With command syntax, MATLAB passes all inputs as character vectors (that is, as if they were enclosed in single quotation marks) and does not assign outputs to variables. To pass a data type other than a character vector, use the function syntax. To pass a value that contains a space, you have two options. One is to use function syntax. The other is to put single quotes around the value. Otherwise, MATLAB treats the space as splitting your value into multiple inputs.

If a value is assigned to a variable, you must use function syntax to pass the value to the function. Command syntax always passes inputs as character vectors and cannot pass variable values. For example, create a variable and call thedispfunction with function syntax to pass the value of the variable:

A = 123; disp(A)

This code returns the expected result,

123

You cannot use command syntax to pass the value ofA, because this call

dispA

相当于

disp('A')

and returns

A

Avoid Common Syntax Mistakes

Suppose that your workspace contains these variables:

filename = 'accounts.txt'; A = int8(1:8); B = A;

The following table illustrates common misapplications of command syntax.

whos -file durer.mat X

whos('-file','durer.mat','X')

HowMATLABRecognizes Command Syntax

Consider the potentially ambiguous statement

ls ./d

This could be a call to thelsfunction with'./d'as its argument. It also could represent element-wise division on the arrayls, using the variabledas the divisor.

If you issue this statement at the command line, MATLAB can access the current workspace and path to determine whetherlsanddare functions or variables. However, some components, such as the Code Analyzer and the Editor/Debugger, operate without reference to the path or workspace. When you are using those components, MATLAB uses syntactic rules to determine whether an expression is a function call using command syntax.

一般来说,当MATLAB承认一个标识符(which might name a function or a variable), it analyzes the characters that follow the identifier to determine the type of expression, as follows:

Therefore, MATLAB treats the potentially ambiguous statementls ./das a call to thelsfunction using command syntax.

The best practice is to avoid defining variable names that conflict with common functions, to prevent any ambiguity.