MATLAB: How to create an array of file pointers for code generation in MATLAB 7.14 (R2012a) using MATLAB Coder 2.2

matlab coder

I have read in the documentation that one can create a file pointer using:

fp = coder.opaque('FILE *', 'NULL')

and that CODER.OPAQUE does not support the creation of arrays, but I would like to create an array of file pointers so that I can index the variable, i.e. fp(1).

Best Answer

The below information is available for R2012b at the following link:

http://www.mathworks.com/help/releases/R2012b/coder/ref/coder.opaque.html

Creating an array of file pointers directly with CODER.OPAQUE is not currently supported in MATLAB 7.14 (R2012a) using MATLAB Coder 2.2.

As a workaround you can create an array of file pointers by combining the CODER.OPAQUE and REPMAT commands as follows:

fp = repmat(coder.opaque('FILE *', 'NULL'),1,size);

Where size is the number of file pointers you wish to create in the array. The variable fp is not dynamically expandable, however it can be indexed with standard MATLAB syntax, i.e. fp(1) is the first file pointer, etc.

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MATLAB: Can I create a dynamic array with the mwArray class of the MATLAB Compiler 4.1 (R14SP1) C++ Utility Library

It is possible to create dynamic arrays with the mwArray class in MATLAB Compiler 4.1 (R14SP1). Below is an example (testme.cpp) that will let the user define the size of 2 arrays:

#include "mclcppclass.h"
int main(){
      if (!mclInitializeApplication(NULL,0))
      {   std::cerr << "could not initialize the library properly"<<std::endl;
           return -1;
      }  
      try
      {   int x,y;
          int* a = NULL;
          int* b = NULL;              
          std::cout << "Enter length of array 1:" <<std::endl;
          std::cin >> x;          // Create input data
          std::cout << "Enter length of array 2:" <<std::endl;
          std::cin >> y;
          a = new int[x]; // Allocate x ints and save ptr in a.
          b = new int[y]; // Allocate y ints and save ptr in b.     
          for (int i=0; i<x; i++) {
              a[i] = i;    // Initialize all elements in increments of 1.
          }    
          for (int j=0; j<y; j++) {
              b[j] = 1;    // Initialize all elements to one.
          }    
          mwArray in1(1, x, mxDOUBLE_CLASS, mxREAL);
          mwArray in2(1, y, mxDOUBLE_CLASS, mxREAL);         
          in1.SetData(a, x);
          in2.SetData(b, y);        
          std::cout << "The 1st array is:" << std::endl;
          std::cout << in1 << std::endl;      
          std::cout << "The 2nd array is:" << std::endl;
          std::cout << in2 << std::endl;        
          delete [] a;  //When done free memory pointed to by a.
          a = NULL; 
          delete [] b;
          b = NULL;     //When done, free memory pointed to by b.
      }
      catch (const mwException& e)
      {   std::cerr << e.what() << std::endl;
          return -1;        
      }
      catch (...)
      {  std::cerr << "Unexpected error thrown" << std::endl;
          return -1;
      }   
      mclTerminateApplication();
      return 0;
   }

You can compile this example using the following command:

mbuild -v testme.cpp

MATLAB: How to use a coder.opaque value in a Matlab expression with codegen

Note that as of MATLAB R2013a fopen, fclose, and fprintf are supported for codegen. Other file I/O functions have been added more recently so you may just be able to use those directly in MATLAB without using coder.ceval at all.

If you decide to use coder.ceval, you can do this:

fp = coder.opaque('FILE *', 'NULL');
fp = coder.ceval('fopen',...);
NULL = coder.opaque('FILE *', 'NULL');
if fp == NULL
  % Something went wrong
else
  % All good
end

Best Answer

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MATLAB: Can I create a dynamic array with the mwArray class of the MATLAB Compiler 4.1 (R14SP1) C++ Utility Library

MATLAB: How to use a coder.opaque value in a Matlab expression with codegen

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