C Caller

Integrate C code in Simulink

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Libraries:
Simulink / User-Defined Functions

Description

The C Caller block integrates your external C code into Simulink^®. This block imports and lists the functions in your external C code, and enables you to select your resolved C functions to integrate in your Simulink models.

Fetch a C Caller block to the Simulink canvas, using Library Browser > Simulink > User Defined Functions.

Then, click the icon on the block dialog box. This opens the Configuration Parameters dialog box. Inside the Configuration Parameters dialog box, go to the Simulation Target pane and use the parameters in the Code information tab to define source code and any supporting files. To browse the function definitions in your source code, use the icon. For more information about defining source code and supporting files, see Specify and Configure Custom C/C++ Code.

To change your source code and the supporting files, use the same parameters in the Code information tab of the Simulation Target pane in the Configuration Parameters dialog box. After changing your source code and the supporting files, refresh the list of functions by clicking the icon on the block dialog box.

Examples

Manually Add and Delete Global Variables from External C Code into Simulink

How to manually add and delete global variables from external C code into Simulink.

• Open Live Script

Use Simulink Strings for C Caller Block

How to use Simulink Strings for C Caller block.

• Open Live Script

Call Custom C Functions in Simulink Using C Caller Block

Call and integrate custom C function that performs arithmetic operations into Simulink.

• Open Live Script

Call C Function Containing C Structure into Simulink

Call and integrate custom C function that performs bus operations into Simulink.

• Open Live Script

Call C Function Containing Enumerated Data Type into Simulink

Map enumerated data type from custom C code into Simulink using a C Caller block.

• Open Live Script

Observe C Caller Block Exported Global Variables Without Model Modification

How to observe exported global variables from C Caller block without displaying those on model canvas.

• Open Live Script

Limitations

• Initialization/Termination of Custom Code Settings — If you need to allocate and deallocate memory for your custom code, insert allocate and deallocate in the Initialize function and Terminate function fields of custom code settings, or use a C Function block.

• Complex Data Support — The block does not support complex data types in Simulink.

• Variable Arguments — Variable arguments in C are not supported, for example, int sprintf(char *str, const char *format, ...).

• C++ Syntax — The block does not support native C++ syntax directly. You need to write a C function wrapper to interface with C++ code.

• Simulink Test™ Observer Support — Starting in R2026a, you can observe exported global variables in a C Caller block using Observer Port and Observer Reference blocks. You cannot use these blocks to observe static global variables or global variables of n-D matrices.

Ports

Input

Port_1 — Input port

scalar | vector | matrix

The number of input ports and their names are inferred through the selected function in your external C code. To provide data to a C Caller block, connect an input signal to the input ports.

The input label has the same name as your input port unless changed by editing the Label column under Port Specification from the Block Dialog. If you rename the label to an input port, the C Caller block changes the name of the port.

For input variables, you can change the input scope to parameters or constants using the Scope column.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | fixed point | enumerated | bus | string

Output

Port_1 — Output port

scalar | vector | matrix

The number of output ports and their names are inferred through the selected function in your external C code. To send data from your C Caller block, connect a block to the output port of your C Caller block.

The output port label has the same name as your output port unless you change it by editing the Label column under Port Specification from the Block Dialog. If you rename the label to an input port, the C Caller block changes the name of the port.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | enumerated | bus | string

Parameters

Function name — Name of function

character vector | string scalar

Name of the function parsed for the C Caller block, specified as a character vector or string scalar. For a list of available functions, see Available Functions.

Tunable: Yes

Programmatic Use

Block Parameter: FunctionName

Type: character vector or string scalar

myFunctionName = get_param(gcb,"FunctionName")

myFunctionName =

    'mean_filter'

Port specification — Port properties

table

Port properties, specified as a table. The table indicates the attributes of each input and output element of the block. If the scope is an input, you can modify this variable to a parameter or a constant. These properties include

Global arguments — Starting in R2026a, you can use buttons in the C Caller block dialog box to add, delete or automatically infer global variables from external custom code. To use these buttons, in the Configuration Parameters dialog box, select Simulation Target. On the Import settings tab, ensure that the Automatically infer global variables as function interfaces checkbox is not selected.

• Add a global variable from external C code to the block using the button. Using this button, you can add one variable at a time. To add global variables programmatically, use the addGlobalArg function, which is available for versions R2024b or later.

• Delete a global variable from the block using the button. To delete a variable, select its row from the Port specification table, and click the button. To delete more than one variable at a time, select the rows corresponding to those variables, and use the button. To delete the global variables programmatically, use the deleteGlobalArg function, which is available for versions R2024b or later.

• To add the global variables used by the selected C function all at once, use the button.

Name — Demonstrates the variable name inferred from your source code.

A bold argument name indicates that the port or parameter is a global argument.

Scope — Indicates the role of the variables from your source code. If the variable is an input argument in the C Caller block source code, you can change the scope type to a constant or a parameter. If the variable is an output argument in the source code, you cannot change the scope type.

Label — Labels the input or output variable for the Simulink model. You can change the labels using this table. If the scope is a parameter, enter the parameter name in this field. If the scope is a constant, enter the constant value.

Type — Indicates the data type coming from the ports.

Size — Indicates the size of the input and output data.

Name, scope, type, and size are inferred from your source code.

Programmatic Use

Block Parameter: FunctionPortSpecification

Type: FunctionPortSpecification object

Available Functions — List of available functions

cell array

List of all available functions that can be mapped to a C Caller block, specified as a cell array.

The C Caller block in your model imports all functions in your external source code, and shows the function names next to the Function name on the block dialog box. To select and use a function in your block, confirm that the function name appears in the Available Functions table. If you are missing one of the functions, reload the source code by clicking button on the block dialog box. To change the names of functions, modify your source code and click the Refresh button to reload.

Programmatic Use

Block Parameter: AvailableFunctions

Type: cell array

allAvailableFunctions = get_param(gcb, "AvailableFunctions")

allAvailableFunctions =

  1×1 cell array

    {'add'}

Sample time — Sample period

-1 (default) | scalar | vector

Sample period, specified in seconds. See Types of Sample Time and Specify Sample Time.

Programmatic Use

Block Parameter: SampleTime

Type: string scalar or character vector

Default: "-1"

Block Characteristics

Data Types	Booleana | busa | doublea | enumerateda | fixed pointa | integera | singlea | stringa
Direct Feedthrough	no
Multidimensional Signals	yesa
Variable-Size Signals	no
Zero-Crossing Detection	no
a Actual data type or capability support depends on block implementation.

More About

Model Coverage

If you have a Simulink Coverage™ license, the C Caller block receives block execution coverage, and the code that the C Caller block calls receives code coverage. When you collect model coverage for a model that contains a C Caller block, Simulink Coverage creates a code coverage report that displays the coverage results for the C code. For more information, see Types of Code Coverage (Simulink Coverage).

Simulink Test Observer

Starting in R2026a, if you have a Simulink Test license, you can use the Observer Port (Simulink Test) and Observer Reference (Simulink Test) blocks to observe the exported global variables used by a C Caller block. These observer blocks allow you to verify and validate exported global variables during simulation without adding extra signal lines to and from the C Caller block. For more information, see Access Model Data Wirelessly by Using Observers (Simulink Test).

Tips

• To test models that include C Caller blocks, see Test Integrated C Code (Simulink Test).

• If a model has custom code, after the model is updated or run, the slprj folder may be locked due to the loaded custom code simulation executable file. You cannot delete the folder when it is locked. To unload the executable file and unlock the slprj folder, use the clear mex command. See clear.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using Simulink® Coder™.

Actual data type or capability support depends on block implementation.

Fixed-Point Conversion
Design and simulate fixed-point systems using Fixed-Point Designer™.

Version History

Introduced in R2018b

R2026a: Simulink Observer support for exported global variables in C Caller block

Starting in R2026a, you can use the Observer Port and Observer Reference blocks to observe exported global variables in a custom code that you integrate using a C Caller block. Use these observer blocks to verify and validate exported global variables without exposing the variables as C Caller block output in the main model.

R2026a: New buttons to add, delete or automatically infer global variables

Starting in R2026a, you can use buttons on the C Caller block dialog box to add and automatically infer global variables from custom code or delete global arguments from the block. These buttons allow you to manage global variables interactively in addition to managing them programmatically using the using the addGlobalArg and deleteGlobalArg functions.

R2024b: Enhancements related to block and function interface

• The block now accepts Simulink strings at its ports when the block calls a C function that uses character pointer (char*) or character array (char[]) as input or output data types.

• You can now use command line APIs to manually add global variables from custom code to the block as global arguments or delete existing global arguments from the block. This enhancement enables you to more directly control the behavior of global variables in the custom code called by the block.