Main Content


Control inlining of a specific function in generated code



coder.inline('always') inlines the current function in the generated code. Use the coder.inline('always') optimization directive to replace a function call with the contents (body) of the called function. Inlining eliminates the overhead of a function call and can create opportunities for further optimization of the generated C/C++ code. However, inlining can generate larger, more complex C/C++ code.

The coder.inline('always') directive does not support the inlining of:

  • entry-point functions.

  • recursive functions.

  • functions that contain parfor loops.

  • functions called from parfor loops.


coder.inline('never') prevents inlining of the current function in the generated code. Use the coder.inline('never') directive when you want to simplify the mapping between the MATLAB® source code and the generated code.

The coder.inline('never') optimization directive does not prevent the inlining of:

  • empty functions.

  • functions that return constant output.

To prevent inlining even in these situations, use the coder.ignoreConst (MATLAB Coder) function on an input at the function call site in your MATLAB code. For more information, see Resolve Issue: coder.inline('never') Does Not Prevent Inlining of Function (MATLAB Coder).

coder.inline('default') instructs the code generator to use internal heuristics to determine whether to inline the current function. Usually, these heuristics produce highly optimized code. Use coder.inline explicitly in your MATLAB functions only when you need to fine-tune these optimizations. For additional guidelines, see Tips (MATLAB Coder).


collapse all

In this example, function foo is not inlined in the generated code:

function y = foo(x)
  y = x;

You can use coder.inline in control flow code. If the software detects contradictory coder.inline directives, the generated code uses the default inlining heuristic and issues a warning.

Suppose that you want to generate code for a division function that runs on a system with limited memory. To optimize memory use in the generated code, the inline_division function manually controls inlining based on whether it performs scalar division or vector division:

function y = inline_division(dividend, divisor)

% For scalar division, inlining produces smaller code
% than the function call itself.  
if isscalar(dividend) && isscalar(divisor)
% Vector division produces a for-loop.
% Prohibit inlining to reduce code size.

if any(divisor == 0)
   error('Cannot divide by 0');

y = dividend / divisor;


  • If you use the codegen (MATLAB Coder) or the fiaccel (Fixed-Point Designer) command, you can disable inlining for all functions by using the -O disable:inline option.

  • If you generate C/C++ code by using the codegen command or the MATLAB Coder™ app, you might have different speed and readability requirements for the code generated for functions that you write and the code generated for MathWorks® functions. Certain additional global settings enable you to separately control the inlining behavior for these two parts of the generated code base and at the boundary between them. See Control Inlining to Fine-Tune Performance and Readability of Generated Code (MATLAB Coder).

Extended Capabilities

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

GPU Code Generation
Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.

Version History

Introduced in R2011a