How do I pass a file path/ string in main.c?

Hello all,

I have created a shared library with MATLAB Coder. With the programme I want to read data from a path, process it and then output the result again. The input for the MATLAB function is therefore a string (char) of the file path and a few more number arguments (double).

To create the .sh, I have compiled the code accordingly in C and would now like to adapt my main.c. To run it in the Linux terminal, I have to create a new main.c.

In order to be able to execute the .sh in the Linux terminal, I adapt my main function as follows:

int main(int argc, char **argv)
{
  char * path =argv[1];
  double rpd;
  double noc;
  rpd = strtol(argv[2],&pEnd_1,10);
  noc = strtol(argv[3],&pEnd_2,10);
  c_main_test_f(path, rpd, noc);
  test_f_terminate();
  return 0;
}

In test_f I then pass the values of the function generated by MATLAB Coder. I have defined two return variables for this:

static void c_main_test_f(char path[], double rtg, double az)
{
   /* This is autogenerated by MATLAB Coder*/
  emxArray_real_T *result_normal;
  emxArray_real_T *result_query;
  emxInitArray_real_T(&result_query, 2);
  emxInitArray_real_T(&result_normal, 2);
  
  printf("Path: %s RTG-value: %f az-value: %f \n", path, rtg, az);
  test_f(path, rtg, az, result_query, result_normal);
  
  emxDestroyArray_real_T(result_query);
  emxDestroyArray_real_T(result_normal);
}

When I compile this now I get the following error:

/home/user/Desktop/lin_file/test_f.h:26:57: note: expected sconst rtString *e {aka rconst struct > *e} but argument is of type schar *t

In the original function (without input parameters) MATLAB Coder suggests me the following for the string/path:

static emxArray_char_T *argInit_1xUnbounded_char_T(void);
static rtString argInit_rtString(void);
static char argInit_char_T(void);

static char argInit_char_T(void)
{
  return '?';
}

static rtString argInit_rtString(void)
{
  rtString result;
  /* Set the value of each structure field.
Change this value to the value that the application requires. */
  result.Value = argInit_1xUnbounded_char_T(pfad_1);
  return result;
}

static emxArray_char_T *argInit_1xUnbounded_char_T(void)
{
  emxArray_char_T *result;
  int idx0;
  int idx1;
  char *result_data;
  /* Set the size of the array.
Change this size to the value that the application requires. */
  result = emxCreate_char_T(1, 2);
  result_data = result->data;
  /* Loop over the array to initialize each element. */
  for (idx0 = 0; idx0 < 1; idx0++) {
    for (idx1 = 0; idx1 < result->size[1U]; idx1++) {
      /* Set the value of the array element.
Change this value to the value that the application requires. */
      result_data[idx1] = argInit_char_T();
    }
  }
  return result;
}

And in c_main_test_f:

/* Befor function call*/
rtString path_name;
path_name = argInit_rtString();

/* After function call*/
emxDestroy_rtString(path_name);

Unfortunately, as I am absolutely no C specialist and also new to MATLAB coders, I have no idea how to pass the file path so that my function can use it.

Can anyone help me here?

Many thanks and best regards

Answer 1

[Tom Engels]

Yes, I can help.

You have to disregard the functions predefined by MATLAB Coder.

Using:

Documantation

and:

Similar question

i was able to convert the string/path/group of chars into the struct.

The command in main.c looks like this:

static void c_main_test_f(char *path, double rtg, double az) {
    emxArray_char_T *path_str;
    /* rows=1, cols = length of the input string */
    path_str = emxCreateWrapper_char_T(path, 1, strlen(path)); 
   
    /* This is autogenerated by MATLAB Coder*/
    emxArray_real_T *result_normal;
    emxArray_real_T *result_query;
    emxInitArray_real_T(&result_query, 2);
    emxInitArray_real_T(&result_normal, 2);
  
    printf("Path: %s RTG-value: %f az-value: %f \n", path, rtg, az);
    test_f(path_str, rtg, az, result_query, result_normal);
    
    emxDestroyArray_real_T(result_query);
    emxDestroyArray_real_T(result_normal);
    emxDestroyArray_real_T(path_str);
}

Also you have to include in main.c:

#include <string.h>
#include <stdio.h>

[Tom Engels]

Now I still have the problem of reading the return values of result_query and result_normal.

My Matlab function returns an array of (n x 3) both times. Where n depends on the size of the read file.

On the one hand, I would like to output this in the terminal and also give this as the return value of the call. (Read the values from emxInitArray_real_T()).

Also, I am not sure if the arrays are initialised correctly. Unfortunately, the documentation is of little help.

-- Docu

void emxInitArray_<name>(emxArray_<name> **pEmxArray, int numDimensions)

Allocates memory for a double pointer to an emxArray.

--

What is meant by "numDimensions"?

Can someone please help me?

[Tom Engels]

numDimensions defines the size of the matrix:

e.g. numDimension = 2 is a struct with (n x n) elements.

One can now simply iterate through this structure, bearing in mind that indexing is done row wise.