External Interfaces

Reference Pointers

Arguments that have more than one level of referencing (e.g., uint16 **) are referred to here as reference pointers. In MATLAB, these argument types are named with the suffix PtrPtr (for example, uint16PtrPtr). See the output of libfunctionsview or methods -full for examples of this type.

When calling a function that takes a reference pointer argument, you can use a reference argument instead and MATLAB will convert it to the reference pointer. For example, the external allocateStruct function expects a c_structPtrPtr argument:

• libfunctions shrlibsample -full
     c_structPtrPtr allocateStruct(c_structPtrPtr)
  

Here is the C function:

• void allocateStruct(struct c_struct **val)
  {
      *val=(struct c_struct*) malloc(sizeof(struct c_struct));
      (*val)->p1 = 12.4;
      (*val)->p2 = 222;
      (*val)->p3 = 333333;
  }
  

Although the prototype says that a c_structPtrPtr is required, you can use a c_structPtr and let MATLAB do the second level of conversion. Create a reference to an empty structure argument and pass it to allocateStruct:

• sp = libpointer('c_structPtr');
  calllib('shrlibsample', 'allocateStruct', sp)
  
  get(sp)
  ans = 
         Value: [1x1 struct]
      DataType: 'c_structPtr'
  
  get(sp, 'Value')
  ans = 
      p1: 12.4000
      p2: 222
      p3: 333333
  

When you are done, return the memory that you had allocated:

• calllib('shrlibsample', 'deallocateStruct', sp)
  

Creating References

Calling C and Fortran Programs from MATLAB

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