C S-function problem when trying to get a pointer to a structure

Question

Leonardo 2012-10-24

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/51766-c-s-function-problem-when-trying-to-get-a-pointer-to-a-structure

回答： Pedro Oliveira 2014-4-28

采纳的回答： Kaustubha Govind

在 MATLAB Online 中打开

Hello all,

I created a structure within the mdlStart method and a pointer to it as follows:

   SomeStructureType  myStruct;
   SomeStructureType* myStruct_ptr;
   myStruct_ptr = &myStruct;

Then I saved the pointer into a (previously defined) PWork vector:

ssSetPWorkValue(S, 0, (void *)myStruct_ptr);

When I retrieve the pointer, within mdlStart, as follows:

anotherStruct_ptr= (SomeStructureType*)ssGetPWorkValue(S,0);

everything works fine. anotherStruct_ptr points to myStruct. But when I try to get the same pointer from the mdlTerminate method, I obtain a wrong one:

   SomeStructureType *Test_ptr;
   Test_ptr = (SomeStructureType*)ssGetPWorkValue(S,0);

Test_ptr does not point to myStruct.

Avoiding the cast gives the same result. I also tried to use ssSetUserData and ssGetUserData instead of ssSetPWorkValue and ssGetPWorkValue, respectively, but the result is still wrong.

I already used PWork vectors without any problem, but this is the first time I use it to hold a pointer to a structure. Am I doing something wrong?

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Kaustubha Govind 2012-10-24

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/51766-c-s-function-problem-when-trying-to-get-a-pointer-to-a-structure#answer_63125

在 MATLAB Online 中打开

You need to use:

SomeStructureType* myStruct_ptr = new SomeStructureType;

to create the pointer. If you simply assign it to a variable on the stack, that memory is free'd at the end of mdlStart, and any further references to it are pointing to corrupt memory and can cause a segmentation violation.

Also, remember to use delete to free that memory in mdlTerminate.

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Leonardo 2012-10-25

编辑：Leonardo 2012-10-25

I completely forgot to allocate the structure!! Thanks!

请先登录，再进行评论。

Answer 2

Pedro Oliveira 2014-4-28

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/51766-c-s-function-problem-when-trying-to-get-a-pointer-to-a-structure#answer_134862

在 MATLAB Online 中打开

Im having a simular problem.

In the mdlStart im doing

 {
  SomeStructureType* myStruct_ptr = new SomeStructureType("Test",0);
  ssSetPWorkValue(S, 0, (void *)myStruct_ptr);
  void * vptr =ssGetPWorkValue(S,0);
  SomeStructureType *Test_ptr;
  Test_ptr = (SomeStructureType*)vptr;
  ssPrintf("%s=%d\n",Test_ptr->info,Test_ptr->counter);
 }

The print out is

Test 0

In the mdlInitializeConditions or mdlUpdate

 {
  void * vptr =ssGetPWorkValue(S,0);
  SomeStructureType *Test_ptr;
  Test_ptr = (SomeStructureType*)vptr;
  ssPrintf("%s=%d\n",Test_ptr->info,Test_ptr->counter);
 }

This gives a segmentation fault.

By looking to the compiler debug attached to Matlab vptr is the correct location (0x00D3A6F0, eg) when we jump between functions but the "recovery" of the class is comletely corrupted.

 Class SomeStructureType 
 {
 public:
  SomeStructureType(std::string _info,int _counter);
  std::string info;
  int counter;
 }
 SomeStructureType::SomeStructureType(std::string _info,int _counter)
 {
  info = _info;
  counter = _counter;
 }