Simulink Model S-Function Generation Gives Error with MSVC Compiler in VS cstring file

Hi

I am using Matlab 2021a

I am getting an error while generating S-function from my simulink model.

I am using Microsoft Visual C++ 2019 (C) for C language compilation.

I created healthy S-functions and their .mex files with this compiler before, but in this Simulink model it gives an error.

While it is creating simModel_sf.c file, in some part it is giving an syntax error in Microsoft Visual Studio 'cstring' file and stops creating .c file and S-function and mex file.

The error message is :

Top model targets built:

Model Action Rebuild Reason

================================================

simModel Failed ForceTopModelBuild was enabled.

0 of 1 models built (0 models already up to date)

Build duration: 0h 8m 34.436s

simModel_sf.c

C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\cstring(21): error C2061: syntax error: identifier 'std'

C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\cstring(21): error C2059: syntax error: ';'

C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\cstring(21): error C2449: found '{' at file scope (missing function header?)

C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\cstring(50): error C2059: syntax error: '}'

C:\Users\Administrator\Desktop\simModelFile\simModel_sfcn_rtw\simModel_sf.c(102309): fatal error C1004: unexpected end-of-file found

and I am copying the cstring file content . The current 'cstring' file content and error creating lines are starting with _STD_BEGIN in 21th line and _STD_END in 50th line.

// cstring standard header (core)

// Copyright (c) Microsoft Corporation.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

#pragma once

#ifndef _CSTRING_

#define _CSTRING_

#include <yvals_core.h>

#if _STL_COMPILER_PREPROCESSOR

#include <string.h>

#pragma pack(push, _CRT_PACKING)

#pragma warning(push, _STL_WARNING_LEVEL)

#pragma warning(disable : _STL_DISABLED_WARNINGS)

_STL_DISABLE_CLANG_WARNINGS

#pragma push_macro("new")

#undef new

_STD_BEGIN

#pragma warning(push)

#pragma warning(disable : 4995) // name was marked as #pragma deprecated

using _CSTD size_t;

using _CSTD memchr;

using _CSTD memcmp;

using _CSTD memcpy;

using _CSTD memmove;

using _CSTD memset;

using _CSTD strcat;

using _CSTD strchr;

using _CSTD strcmp;

using _CSTD strcoll;

using _CSTD strcpy;

using _CSTD strcspn;

using _CSTD strerror;

using _CSTD strlen;

using _CSTD strncat;

using _CSTD strncmp;

using _CSTD strncpy;

using _CSTD strpbrk;

using _CSTD strrchr;

using _CSTD strspn;

using _CSTD strstr;

using _CSTD strtok;

using _CSTD strxfrm;

#pragma warning(pop)

_STD_END

#pragma pop_macro("new")

_STL_RESTORE_CLANG_WARNINGS

#pragma warning(pop)

#pragma pack(pop)

#endif // _STL_COMPILER_PREPROCESSOR

#endif // _CSTRING_

What could be the problem here? Is there maybe a header conflicting from my current path includes with Visual Studio headers?

I tried

mex -setup c

mex -setup cpp but both didn't work. Any help would be much appreciated.

Thank you

Answer 1

[Jack]

This issue appears to be caused by a conflict between MATLAB’s generated code and the Visual Studio 2019 MSVC compiler's standard headers, specifically with the cstring file. Here’s how you can systematically debug and resolve the issue.Possible Causes & Solutions:1. Ensure That the Correct Compiler Version is Set in MATLAB

• Verify that MATLAB is using the correct Microsoft Visual Studio (MSVC) compiler: mex -setup C

mex -setup C++

• If multiple versions of Visual Studio are installed, MATLAB might be picking an incorrect one. To force MATLAB to use a specific version, specify it explicitly: mex -setup C "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\bin\Hostx64\x64\cl.exe"

• Check MATLAB’s recognized compilers using: mex -setup

2. Check for Path Conflicts in Included Headers

• Since the error occurs in the cstring file, it’s possible that there is a conflicting version of a standard C++ library in MATLAB’s include paths.
• Run the following command to inspect the active include paths: getenv('INCLUDE')

• Look for conflicting paths from an older or incompatible library (e.g., MATLAB’s internal MinGW compiler might be conflicting with MSVC).
• If a conflicting path is found, temporarily remove it using: setenv('INCLUDE', '')

• Then, retry building the S-Function.

3. Force MATLAB to Use the Correct Standard Library

Since cstring is a C++ standard library header, check if MATLAB is using incorrect C++ standard settings:

• Open the Simulink Coder Configuration Parameters:
• Go to Model Configuration (Ctrl+E in Simulink) → Code Generation → Custom Code.
• Ensure that the Compiler Flags include -std=c++17 or -std=c++14 (depending on MSVC compatibility).
• Alternatively, modify mex options manually: mex -v -DMATLAB_MEX_FILE -std=c++17 myfile.c

• Force the compiler to use standard C headers instead of C++ headers:
• Before compiling, add: #include <string.h>

instead of:

#include <cstring>

• Explicitly define _STL_COMPILER_PREPROCESSOR before including cstring:#define _STL_COMPILER_PREPROCESSOR 1

#include <cstring>

4. Ensure That Simulink Is Not Generating Incompatible Code

• Since the error happens during S-function code generation, regenerate the Simulink Coder cache: slprj rebuild

• Delete any old code and rebuild:
• Navigate to your simModelFile\simModel_sfcn_rtw directory and delete any previously generated .c and .mexw64 files.
• Recompile with: slbuild('simModel')

5. Try an Older MSVC Version

• Some users report that MSVC 2017 (v141 toolset) works more reliably with MATLAB R2021a than MSVC 2019.
• If possible, try using an older version:
• Open Visual Studio Installer, go to Modify, and install MSVC v141 toolset.
• Then set MATLAB to use it: mex -setup C "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\bin\Hostx64\x64\cl.exe"

Final Steps

After making the changes, try recompiling your S-Function using:

mex -v simModel_sf.c

If the problem persists, please provide:

• The full compilation log (mex -v output).
• The specific MATLAB-generated code (simModel_sf.c) where the error occurs.

This should help pinpoint the exact issue. Let me know how it goes! 🚀

[Mete Soylu]

Thanks for the quick answer. I applied your suggestions 1,2,4 but I couldn't succeed.

#include <cstring> calls a C++ header because _STD_BEGIN and _STD_END are C++ macros.

I changed Configuration parameters --> Code Generation Settings to

C++ code generation and selected MSVC 2019 C++ compiler

then I wrote to command window

mex -setup C++

with these settings, when I tried auto generation of Simulink on my Simulink subsystem, this time, It didn't give the <cstring> error, it filled more code into simModel.cpp file, but it gave Library Link error. It couldn't find Library named libecatinterface_vcx64.lib

Error is:

LINK : fatal error LNK1181: cannot open input file 'C:\Program Files\Polyspace\R2021a\toolbox\slrealtime\simulink\blocks\dist\lib\libecatinterface_vcx64.lib'

I couldn't find any info about this library on the internet. I think, I am going to change my Visual Studio to older version as you said. That will ,it seems, solve my problem.

Than you so much.

[Jack]

I'm glad I could help if you need any other assistance let me know (follow me to message me directly about any possible future problems) !