Inline State Functions in Generated Code

How Stateflow Software Inlines Generated Code for State Functions

By default, Stateflow® software uses an internal heuristic to determine whether or not to inline state functions in code generated with Simulink® Coder™ software. The heuristic takes into consideration an inlining threshold, so as your code grows and shrinks in size, the generated code for state functions can be unpredictable.

However, if you have rigorous requirements for traceability between generated code and the corresponding state functions, you can override this default behavior. Stateflow software provides a state property Function Inline Option that helps you explicitly force or prevent inlining of state functions.

What Happens When You Force Inlining

If you force inlining for a state, all code generated for its state actions will be inlined into the parent function. The parent function contains code for executing the state actions, outer transitions, and flow charts. It does not include code for empty state actions.

What Happens When You Prevent Inlining

If you prevent inlining for a state, Simulink Coder software generates the following static functions, as in this example for state foo:



Marks foo active and performs entry actions


Calls default paths


Executes flow charts that originate when an inner transition and default transition reach the same junction inside a state.

Stateflow software generates this function only when the flow chart is complex enough to exceed the inlining threshold.

In generated code, Stateflow software calls this function from both the enter_internal_foo and foo functions.


Checks for valid outer transitions and if none, performs during actions


Performs exit actions and marks foo inactive


Performs exit actions of the child substates and then exits foo

Suppose that you explicitly prevent inlining for the following state A in model M:

Stateflow software generates the following functions:

static void M_inner_default_A(void);
static void M_exit_atomic_A(void);
static void M_A(void);
static void M_enter_atomic_A(void);
static void M_enter_internal_A(void);

How to Set the State Function Inline Option

To set the function inlining property for a state:

  1. Right-click inside the state and select Properties from the context menu.

    The State properties dialog box opens.

  2. In the Function Inline Option field, select one of these options:

    InlineForces inlining of state functions into the parent function, as long as the function is not part of a recursion. See What Happens When You Force Inlining.
    FunctionPrevents inlining of state functions. Generates up to six static functions for the state. See What Happens When You Prevent Inlining.
    AutoUses internal heuristics to determine whether or not to inline the state functions.

  3. Click Apply.

Best Practices for Controlling State Function Inlining

To...Set the Function Inline Option property to...
Generate a separate function for each action of a state and a separate function for each action of its substatesFunction for the state and each substate
Generate a separate function for each action of a state, but include code for the associated action of its substatesFunction for the state and Inline for each substate

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