Call C Library Functions

You can add mathematical operations, trigonometric calculations, and exponential computations, or call C functions in your Stateflow® charts by calling C library functions. Charts that use C as the action language can call C library functions without using any special prefixs or function wrappers. To call C functions in charts that use MATLAB® as the action language, use the coder.ceval (Simulink) function. For more information, see Integrate C Code by Using the MATLAB Function Block (Simulink).

To update the action language that your chart uses, see Modify the Action Language for a Chart.

Calling C Library Functions

In charts that use C as the action language, you can call these C math library functions:

  • abs

  • sin

  • cos

  • tan

  • sinh

  • tanh

  • acos

  • atan

  • atan2

  • cosh

  • ceil

  • floor

  • exp

  • fabs

  • fmod

  • labs

  • ldexp

  • log

  • log10

  • pow

  • rand

  • sqrt

When you call these functions, you must use double-precision values unless all the input arguments are explicitly single precision. When the input arguments do not match, the chart casts the input arguments to the expected data type. For example, if youc all the sin function with an integer as an input argument, the chart casts the input argument to a floating-point number of type double.

To call other C library functions, open the Configuration Parameters dialog box and, in the Simulation Target pane, enter the appropriate #include statements, as described in Configure Custom Code.

Note

When a chart casts the input arguments to the C library functions to floating-point numbers, function calls with arguments of type int64 or uint64 can result in loss of precision.

Calling the abs Function

Stateflow charts interpret the abs function differently than the standard C version of abs by processing integer and floating-point arguments as follows:

  • If x is an integer of type int32 or int64, the standard C function abs applies to x, or abs(x).

  • If x is an integer of type int16 or int8, the standard C abs function applies to a cast of x as an integer of type int32, or abs((int32)x).

  • If x is a floating-point number of type double, the standard C function fabs applies to x, or fabs(x).

  • If x is a floating-point number of type single, the standard C function fabs applies to a cast of x as a double, or fabs((double)x).

  • If x is a fixed-point number, the standard C function fabs applies to a cast of the fixed-point number as a double, or fabs((double) Vx), where Vx is the real-world value of x.

If you want to use the abs function as it works in the standard C versionof the function, cast its argument or return values to integer types. For more information, see Type Cast Operations.

Note

If you declare a variable in custom code, the standard C abs function applies in all cases. For instructions on inserting custom code into charts, see Use Custom C or C++ Code in Stateflow Charts.

Calling min and max Functions

You can call min and max by emitting these macros at the top of generated code.

#define min(x1,x2) ((x1) > (x2) ? (x2):(x1))
#define max(x1,x2) ((x1) > (x2) ? (x1):(x2))

To allow compatibility with user-created graphical functions named min() or max(), the functions in the generated code use the name <prefix>_min. However, if you export min() or max() graphical functions to other charts in your model, the generated code cannot use the modified name for the functions, and and conflict occurs. To avoid this conflict, rename the min() and max() graphical functions.

Replacing Math Library Functions with Application Implementations

With the exception of labs and rand, you can change how the code generator implements math library functions in the final generated code. To do this, you configure the code generator to apply a code replacement library (CRL) during code generation. Additionally, you can develop custom CRLs if you have an Embedded Coder® license.

For more information about replacing code using the CRLs that MathWorks® provides, see What Is Code Replacement? (Simulink Coder) and Code Replacement Libraries (Simulink Coder). For information about developing custom code replacement libraries, see What Is Code Replacement Customization? (Embedded Coder) and Code You Can Replace From Simulink Models (Embedded Coder).

Calling Custom C Code Functions

You can create custom C functions in Stateflow charts and use them for simulation and code generation. When calling custom functions:

  • Write the function name, followed by the arguments in parentheses.

  • End the function call with an optional semicolon.

  • Pass parameters to user-written functions using single quotation marks.

  • Use double quotation marks for text strings.

C functions can return any data type. For more information, see Configure Custom Code. When you write C functions that access input vectors:

  • Use the sizeof function to determine the length of an input vector.

    For example, your custom function can include a for-loop that uses sizeof, enter:

    for(i=0; i < sizeof(input); i++) {
......
}

  • If your custom function uses the value of the input vector length multiple times, include an input to your function that specifies the input vector length.

    For example, you can use input_length as the second input to a sum function as follows:

    int sum(double *input, double input_length)

    To include a for-loop in the sum function that iterates over all elements of the input vector, enter:

    for(i=0; i < input_length; i++) {
......
}

Using Function Calls in Transition Actions

This chart uses C function calls in the transition actions.

Chart that contains transition actions with calls to custom code functions fcn1 and fcn2.

A function call to fcn1 occurs with arg1, arg2, and arg3 if these conditions are true:

  • S1 is active.

  • Event e occurs.

  • Condition c is true.

  • The transition destination S2 is valid.

Additionally, the transition action in the transition from S2 to S3 shows an example of a function call nested in another function call.

Using Function Calls in State Actions

This chart uses function calls in the state actions.

Chart that contains state actions with calls to custom code functions fcn1 and fcn2.

When the chart executes:

  1. The default transition to S1 occurs, and S1 becomes active.

  2. The entry action, which is a function call to fcn1 with the specified arguments, executes.

  3. After five seconds of simulation time, S1 becomes inactive and S2 becomes active.

  4. The during action, which is a function call to fcn2 with the specified arguments, executes.

  5. After 10 seconds of simulation time, S2 becomes inactive and S1 becomes active again.

  6. Steps 2 through 5 repeat until the simulation ends.

Passing Arguments by Reference

A chart action can pass arguments to a user-written function by reference rather than by value. For example, an action can contain the function call:

f(&x);

where f is a custom-code C function that expects a pointer to x as an argument.

If x is the name of a data item in the Stateflow hierarchy, these rules apply:

  • Do not use pointers to pass data items input from a Simulink® model.

    If you need to pass an input item by reference, such as an array, assign the item to a local data item and pass the local item by reference.

  • If the data type of x is boolean, you must turn off the model configuration parameter Use bitsets for storing state configuration.

  • If x is an array and the first index property is 0, you must call the function by using f(&(x[0]));. This syntax passes a pointer to the first element of x to the function. See Set Data Properties.

  • If x is an array and the first index property is a nonzero number, you must call the function by using f(&(x[1])). This syntax passes a pointer to the first element of x to the function.

See Also

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