setdatatype from void* to structPtr

I have C code which is defining structs and some basic functions:

#include <mex.h> 
#include "tst.h"

void mexFunction( int nlhs, mxArray *plhs[], 
          int nrhs, const mxArray*prhs[] )
{
}

EXPORTED_FUNCTION S_another* returnStructPtr_explicit(S_input* arg){
  return &arg->world;
}

EXPORTED_FUNCTION void* returnFloatPtr(S_input* arg){
  arg->fnum=5.1;
    arg->world.please = 5;
  return &arg->fnum;
}

EXPORTED_FUNCTION void* returnStructPtr(S_input* arg){
  return &arg->world;
}

And the Header file:

#ifndef _TST_H_
#define _TST_H_

#define EXPORT_FCNS

#ifdef EXPORT_FCNS
#define EXPORTED_FUNCTION __declspec(dllexport)
#else
#define EXPORTED_FUNCTION __declspec(dllimport)
#endif

typedef struct S_another
{
  int please;
  int help;
  int to_solve;
  int my_problem;
  
} S_another;

typedef struct S_input
{
  float fnum;
  S_another world;
  
} S_input;

EXPORTED_FUNCTION S_another* returnStructPtr_explicit(S_input* arg);
EXPORTED_FUNCTION void* returnFloatPtr(S_input* arg);
EXPORTED_FUNCTION void* returnStructPtr(S_input* arg);
#endif

After mexing and loading the library, the first 2 functions work well:

[a,b] = calllib('tst','returnStructPtr_explicit',sc);
a.Value

and

[a,b] = calllib('tst','returnFloatPtr',sc);
% Casting the datatype according to float
setdatatype(a,'singlePtr',1,1)

but the third function fails (at setdatatype) and crashes matlab:

[a,b] = calllib('tst','returnStructPtr',sc);
% for struct pointer value
setdatatype(a,'S_anotherPtr',1,1)

Any help will be greatly appreciated. Thanks