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assert

Throw error if condition false

Syntax


            
             assert(cond)


            
             assert(cond,msg)


            
             assert(cond,msg,A)


            
             assert(cond,errID,msg)


            
             assert(cond,errID,msg,A)

Description

assert( cond ) throws an error if cond is false.

example

assert( cond , msg ) throws an error and displays the error message, msg , if cond is false.

example

assert( cond , msg , A ) displays an error message that contains formatting conversion characters, such as those used with the MATLAB ^® sprintf function, if cond is false. Each conversion character in msg is converted to one of the values

assert( cond , errID , msg ) throws an error, displays the error message, msg , and includes an error identifier on the exception, if cond is false. The identifier enables you to distinguish errors and to control what happens when MATLAB encounters the errors.

example

assert( cond , errID , msg , A ) includes an error identifier on the exception and displays a formatted error message.

Examples

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Value in Expected Range

Assert that the value, x , is greater than a specified minimum value.

minVal = 7;
x = 26;
assert(minVal < x)

The expression evaluates as true, and the assertion passes.

Assert that the value of x is between the specified minimum and maximum values.

maxVal = 13;
assert((minVal < x) && (x < maxVal))

Error using assert
Assertion failed.

The expression evaluates as false. The assertion fails and MATLAB throws an error.

Expected Data Type

Assert that the product of two numbers is a double-precision number.

a = 13;
b = single(42);
c = a*b;
assert(isa(c,'double'),'Product is not type double.')

Error using assert
Product is not type double.

Enhance the error message to display the data type of c .

assert(isa(c,'double'),'Product is type %s, not double.',class(c))

Error using assert




    

Product is type single, not double.

Expected Code Conditions

Use the assert function to test for conditions that should not happen in normal code execution. If the coefficients are numeric, the computed roots should be numeric. A quadratic equation using the specified coefficients and computed roots should be zero.

function x = quadraticSolver(C)
validateattributes(C,{'numeric'},{'size',[1 3]})
a = C(1);
b = C(2);
c = C(3);
x(1) = (-b+sqrt(b^2-4*a*c))/(2*a);
x(2) = (-b-sqrt(b^2-4*a*c))/(2*a);
assert(isnumeric(x),'quadraticSolver:nonnumericRoots',...
    'Computed roots are not numeric')
y1 = a*x(1)^2+b*x(1)+c;
y2 = a*x(2)^2+b*x(2)+c;
assert(y1 == 0,'quadraticSolver:root1Error','Error in first root')
assert(isequal(y2,0),'quadraticSolver:root2Error','Error in second root')
end

Input Arguments

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`cond` — Condition to assert
MATLAB expression

Condition to assert, specified as a valid MATLAB expression. This expression must be logical or convertible to a logical. If cond is false, the assert function throws an error. cond can include relational operators (such as < or == ) and logical operators (such as && , || , or ~ ). Use the logical operators and and or to create compound expressions. MATLAB evaluates compound expressions from left to right, adhering to operator precedence rules.

Example: a<0

Example: exist('myfunction.m','file')

`msg` — Information about assertion failure
character vector | string scalar

Information about the assertion failure, specified as a character vector or string scalar. This message displays as the error message. To format the message, use escape sequences, such as \t or \n . You also can use any format specifiers supported by the sprintf function, such as %s or %d . Specify values for the conversion specifiers via the A1,...,An input arguments. For more information, see Formatting Text .

Note

You must specify more than one input argument with assert if you want MATLAB to convert special characters (such as \t , \n , %s , and %d ) in the error message.

Example: 'Assertion condition failed.'

`A` — Replacement value
character vector | string scalar | numeric scalar

Value that replace the conversion specifiers in msg , specified as a character vector, string scalar, or numeric scalar.

`errID` — Identifier for assertion failure
character vector | string scalar

Identifier for the assertion failure, specified as a character vector or string scalar. Use the identifier to help identify the source of the error or to control a selected subset of the errors in your program.

The error identifier includes one or more component fields and a mnemonic field. Fields must be separated with colon. For example, an error identifier with a component field component and a mnemonic field mnemonic is specified as 'component:mnemonic' . The component and mnemonic fields must each begin with a letter. The remaining characters can be alphanumerics (A–Z, a–z, 0–9) and underscores. No white-space characters can appear anywhere in errID . For more information, see MException .

Example: 'MATLAB:singularMatrix'

Example: 'MATLAB:narginchk:notEnoughInputs'

Tips

When you issue an error, MATLAB captures information about it and stores it in a data structure that is an object of the MException class. You can access information in the exception object by using try/catch . Or, if your program terminates because of an exception and returns control to the Command Prompt, you can use MException.last .
If an assertion failure occurs within a try block, MATLAB does not cease execution of the program. In this case, MATLAB passes control to the catch block.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

Generates specified error messages at compile time only if all input arguments are constants or depend on constants. Otherwise, generates specified error messages at run time.
If called with more than 1 argument, has no effect in standalone code even when run-time error detection is enabled. See Generate Standalone C/C++ Code That Detects and Reports Run-Time Errors (MATLAB Coder) .
To use the assert function to specify properties of primary function inputs or set preconditions on primary function inputs, see Rules for Using assert Function (MATLAB Coder) .

Thread-Based Environment
Run code in the background using MATLAB® `backgroundPool` or accelerate code with Parallel Computing Toolbox™ `ThreadPool` .

This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment .

GPU Arrays
Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

The assert function supports GPU array input with these usage notes and limitations:

This function accepts GPU arrays, but does not run on a GPU.

For more information, see Run MATLAB Functions on a GPU (Parallel Computing Toolbox) .

Version History

Introduced in R2007a

expand all

R2022a: Output displays which assertion threw an error and the location in the code

When an assertion fails, the error thrown includes the specific assertion that failed and the location in the code.

assert

Syntax

Description

Examples

Value in Expected Range

Expected Data Type

Expected Code Conditions

Input Arguments

cond — Condition to assert MATLAB expression

msg — Information about assertion failure character vector | string scalar

A — Replacement value character vector | string scalar | numeric scalar

errID — Identifier for assertion failure character vector | string scalar

Tips

Extended Capabilities

C/C++ Code Generation Generate C and C++ code using MATLAB® Coder™.

Thread-Based Environment Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool .

GPU Arrays Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

Version History

R2022a: Output displays which assertion threw an error and the location in the code

See Also

`cond` — Condition to assert
MATLAB expression

`msg` — Information about assertion failure
character vector | string scalar

`A` — Replacement value
character vector | string scalar | numeric scalar

`errID` — Identifier for assertion failure
character vector | string scalar

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Thread-Based Environment
Run code in the background using MATLAB® `backgroundPool` or accelerate code with Parallel Computing Toolbox™ `ThreadPool` .

GPU Arrays
Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.