Stand alone C file

I have my matlab code which is working, but a little slow. I want to write it for C, but I have an error that comes up when I use the Code Generation Rediness test. I am using

y(1) = dlmread('filename.txt');

and

y(n) = dlmwrite('newfilename.txt');

in a for loop that goes from 1 to n. The Readiness test says that these won't work, but I don't know how to read these text files into the code in a way that will be able to convert into C. The files are 201x201 arrays.

If anyone can help me out, it would be much appreciated

Answer 1

[Ryan Livingston]

One way to do this is to use coder.ceval and the C runtime functions. Alternatively, the MATLAB functions FOPEN, FREAD, FCLOSE are all supported for code generation. So you could use those to read the file in to a MATLAB string, and then use coder.ceval to call sscanf to parse the string.

There is an example in the doc that demonstrates reading a file using coder.ceval.

If you want to use the C runtime, and supposing that the file is named data.txt and that it contains 201-by-201 (201 lines of 201) space-delimited doubles (e.g. output from dlmwrite('data.txt',reshape(1:(201^2),201,201),'delimiter',' '); ) you could use something like:

    function y = parsefile
    %#codegen
    coder.cinclude('<stdio.h>');
    f = coder.opaque('FILE*','NULL');
    f = coder.ceval('fopen', cstr('data.txt'),cstr('r'));
    assert(f ~= coder.opaque('FILE*','NULL'), 'Failed to open file');

    % Parse file
    N = 201;
    y = coder.nullcopy(zeros(N,N));
    fmt = cstr('%lf ');
    for k = 1:numel(y)
        coder.ceval('fscanf', f, fmt, coder.wref(y(k)));
    end
    coder.ceval('fclose',f);

    % File was read in row-major order so transpose
    y = y.';

    %--------------------------------------------------------------------------

    function s = cstr(st)
    % Append a \0 (NUL) character to produce a C
    % string from a MATLAB string
    s = [st, 0];

Just run:

codegen parsefile
y = parsefile_mex;

to use it.

Answer 2

[Youssef Khmou]

If you mean reading a file with C, then you need to use pointer as the following, with apriori knowledge of array dimensions :

 #include <stdio.h>
 int main(void)
{
      int x=201;
      int y=201;
      FILE *yourfile=NULL;
      char c;
      int i=0,j=0;
      double M[x][y];
      yourfile = fopen("filename.txt","r");
      c = getc(yourfile) ;
      while (c!= EOF)
        {
           M[i][j]=c;
           j++;
           c = getc(fp);
           if(j==201){
                  i++;
                  j=0;
                     }
        }
fclose(yourfile);
}