str2func

Construct function handle from character vector

Description

example

fh = str2func(str) constructs a function handle, fh, from a function name or text representation of an anonymous function.

Function handles created using str2func do not have access to variables outside of their local workspace or to nested functions. If your function handle contains these variables or functions, MATLAB® throws an error when you invoke the handle. Also, if you use a text representation of an anonymous function, the resulting function handle does not have access to private or local functions.

Examples

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Convert the character vector 'ones' to a function handle, and call the ones function using the handle.

c = 'ones';
fh = str2func(c)
fh = function_handle with value:
@ones

fh(1,5)
ans = 1×5

1     1     1     1     1

Convert a character vector that represents an anonymous function to a function handle. Workspace variables are not available to the str2func function. Therefore, include values in the character vector that are necessary to evaluate the expression and that are not defined as function inputs.

Define a character vector that represents the anonymous function 7x – 13. Convert the character vector to a function handle.

str = '@(x)7*x-13';
fh = str2func(str)
fh =

@(x)7*x-13

Call the anonymous function using the handle.

fh(3)
ans =

8

If you include workspace variables in your character vector, str2func creates the function handle, but MATLAB throws an error when you invoke the function handle.

a = 13;
str = '@(x)7*x-a';
fh = str2func(str);

fh(3)
Undefined function or variable 'a'.

Error in @(x)7*x-a

Create a function that returns two function handles used to simulate the roll of dice. The first die (d1) returns a number from 1 through 6, but the second die (d2) always returns the number 1.

Create the following function in a folder on your MATLAB path. When str2func is used with a character vector representing an anonymous function, it does not have access to the local function. Therefore, MATLAB calls the built-in randi function, and returns a number from 1 through 6. The eval function does have access to the local function, so d2 uses the overloaded randi and always returns 1.

function [d1,d2] = diceRoll
str = '@()randi([1 6],1)';
d1 = str2func(str);
d2 = eval(str);
end

function r = randi(~,~)
r = 1;
end

At the command prompt, call the diceRoll function.

[p1,p2] = diceRoll
p1 =

function_handle with value:

@()randi([1,6],1)

p2 =

function_handle with value:

@()randi([1,6],1)

Both p1 and p2 appear to be associated with the same anonymous function.

Invoke the function handles. The result from p1 varies from 1 through 6. The result from p2 is always 1.

p1()
p2()
ans =

5

ans =

1

Input Arguments

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Text to convert to a function handle, specified as a function name or a character vector or string scalar representation of an anonymous function.

Example: str = 'cos'

Example: str = '@(x) x.^2'

Tips

• A function handle that stores variable values does not retain its original value when you use func2str to convert it to a character vector, and then convert it back to a handle with str2func.