Unknown Output Type for coder.ceval

Issue

You see this error message:

Output of 'coder.ceval' has unknown type. The enclosing expression cannot be evaluated. Specify the output type by assigning the output of 'coder.ceval' to a variable with a known type.

Cause

This error message occurs when the code generator cannot determine the output type of acoder.cevalcall.

Solution

Initialize a temporary variable with the expected output type. Assign the output ofcoder.cevalto this variable.

Example

Assume that you have a C function calledcFunctionThatReturnsDouble. You want to generate C library code for a functionfoo. The code generator returns the error message because it cannot determine the return type ofcoder.ceval.

functionfoo%#codegencallFunction(coder.ceval('cFunctionThatReturnsDouble'));endfunctioncallFunction(~)end

To fix the error, define the type of the C function output by using a temporary variable.

functionfoo%#codegentemp = 0; temp = coder.ceval('cFunctionThatReturnsDouble'); callFunction(temp);endfunctioncallFunction(~)end

You can also usecoder.opaqueto initialize the temporary variable.

Example Using Classes

假设您有一个类和一个定制的setmethod. This class uses thesetmethod to ensure that the object property value falls within a certain range.

classdefclassWithSetterpropertiesexpectedResult = []endproperties(Constant) scalingFactor = 0.001endmethodsfunctionobj = set.expectedResult(obj,erIn)iferIn >= 0 && erIn <= 100 erIn = erIn.*obj.scalingFactor; obj.expectedResult = erIn;elseobj.expectedResult = NaN;endendendend

When generating C library code for the functionfoo, the code generator produces the error message. The input type into thesetmethod cannot be determined.

functionfoo%#codegenobj = classWithSetter; obj.expectedResult = coder.ceval('cFunctionThatReturnsDouble');end

To fix the error, initialize a temporary variable with a known type. For this example, use a type of scalar double.

functionfoo%#codegenobj = classWithSetter; temp = 0; temp = coder.ceval('cFunctionThatReturnsDouble'); obj.expectedResult = temp;end