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Function Definition

Defining and calling functions for code generation

There are special considerations when you create MATLAB® functions that are intended for code generation. These include certain restrictions when you use varargin and varargout, recursive functions, anonymous functions, and nested functions. To generate code for MATLAB recursive functions, the code generator uses either compile-time recursion or run-time recursion. To produce efficient C/C++ code, the code generator sometimes creates multiple versions of a function, referred to as function specializations. In certain cases, you can prevent the code generator from creating function specializations by using coder.ignoreConst and coder.ignoreSize. While generating a MEX function, you can bypass code generation for a specific function in your MATLAB code and instead use the MATLAB engine to execute the call. To do this, use the coder.extrinsic construct.


coder.extrinsicDeclare function as extrinsic and execute it in MATLAB
coder.ignoreConstPrevent use of constant value of expression for function specializations
coder.ignoreSizePrevent code generator from creating function specializations for constant-size expressions (Since R2019b)
coder.mustBeComplexValidate that value lies on the complex plane (Since R2023b)
coder.mustBeConstValidate that value is a compile-time constant (Since R2023b)
coder.noImplicitExpansionInFunctionDisable implicit expansion within the specified function in the generated code (Since R2021b)
coder.sameSizeBinaryOpApply element-wise binary operations without implicit expansion (Since R2021b)
coder.specifyAsGPUSpecify that value is a GPU input to an entry-point function for GPU code generation (Since R2023b)



Nonconstant Index into varargin or varargout in a for-Loop

Force loop unrolling when the code generator cannot determine the value of the index into varargin or varargout.

Avoid Duplicate Functions in Generated Code

Reduce the occurrence of duplicate functions in the generated code.

Output Variable Must Be Assigned Before Run-Time Recursive Call

Troubleshoot output variable assignment for run-time recursion.

Compile-Time Recursion Limit Reached

Troubleshoot compile-time recursion limit error.

Resolve Error: Size Mismatches

Troubleshoot size mismatch errors that occur during code generation.

Resolve Issue: coder.inline("never") and coder.nonInlineCall Do Not Prevent Function Inlining

Troubleshoot instances of coder.inline('never') not preventing inlining.

Resolve Issue: Variables Must Be Fully Defined Before Use

Troubleshoot code generation errors when variables, including structure fields and class properties, are not defined before use.