Troubleshoot S-Function Build Upgrade

A pre-R2020b model uses S-Functions. When migrating this model to the current release, this S-Function related message appears in the build log:

undefined reference to 'C function in S-Function'

What This Issue Means

In R2020b and later releases, the compiler for model builds changed from a Windows® compatible C compiler to the C++ compiler. To accommodate this change, update S-Function code for C++ compatibility.

Tip

Fortran S-Functions are not supported in R2020b and later releases of Simulink® Real-Time™.

In R2026a and later releases, support is available for the C++ compiler for target computers using the Linux®-based RTOS. To accommodate this addition, update S-Function code for C++ compatibility.

Try This Workaround

To update S-Function code for C++ compatibility, modify the declaration of the S-Function in the header file.

For example, update this C S-Function declaration:

void getAllDataMyFunction(short);
void myfunction_initialize(short, unsigned char*, short*);
void myfunction_terminate(short, int);

Updated the code to this C++ S-Function declaration:

#ifdef __cplusplus
extern "C" {
#endif

void getAllDataMyFunction(short);
void myfunction_initialize(short, unsigned char*, short*);
void myfunction_terminate(short, int);

#ifdef __cplusplus
}
#endif

Before building the updated code, remove all artifacts from previous model builds.

See Also

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