MATLAB: How to make codegen concatenate strings

Question

Using R2012a codegen, if I create the following m file:

function testStrCat()

path = char(zeros(1, 40));

fspec = char(zeros(1, 132));

coder.ceval('strcat', path, 'path');

coder.ceval('strcat', fspec, path);

coder.ceval('strcat', fspec, '/');

then build it as a C static library, I get the following output file:

 1   /*
    2    * testStrCat.c
    3    *
    4    * Code generation for function 'testStrCat'
    5    *
    6    * C source code generated on: Thu Oct 04 13:47:50 2012
    7    *
    8    */
    9   
   10   /* Include files */
   11   #include "rt_nonfinite.h"
   12   #include "testStrCat.h"
   13   
   14   /* Type Definitions */
   15   
   16   /* Named Constants */
   17   
   18   /* Variable Declarations */
   19   
   20   /* Variable Definitions */
   21   
   22   /* Function Declarations */
   23   
   24   /* Function Definitions */
   25   
   26   /*
   27    * function testStrCat
   28    */
   29   void testStrCat(void)
   30   {
   31     char_T cv0[40];
   32     int32_T i0;
   33     char_T cv1[4];
   34     static const char_T cv2[4] = { 'p', 'a', 't', 'h' };
   35   
   36     char_T cv3[132];
   37   
   38     /* 'testStrCat:2' path = char(zeros(1, 40)); */
   39     /* 'testStrCat:3' fspec = char(zeros(1, 132)); */
   40     /* 'testStrCat:5' coder.ceval('strcat', path, 'path'); */
   41     for (i0 = 0; i0 < 40; i0++) {
   42       cv0[i0] = '\x00';
   43     }
   44   
   45     for (i0 = 0; i0 < 4; i0++) {
   46       cv1[i0] = cv2[i0];
   47     }
   48   
   49     strcat(cv0, cv1);
   50   
   51     /* 'testStrCat:6' coder.ceval('strcat', fspec, path); */
   52     for (i0 = 0; i0 < 132; i0++) {
   53       cv3[i0] = '\x00';
   54     }
   55   
   56     for (i0 = 0; i0 < 40; i0++) {
   57       cv0[i0] = '\x00';
   58     }
   59   
   60     strcat(cv3, cv0);
   61   
   62     /* 'testStrCat:7' coder.ceval('strcat', fspec, '/'); */
   63     for (i0 = 0; i0 < 132; i0++) {
   64       cv3[i0] = '\x00';
   65     }
   66   
   67     strcat(cv3, '/');
   68   
   69     /*  coder.ceval('strcat', fspec, file); */
   70   }
   71   
   72   /* End of code generation (testStrCat.c) */

Notice that each time I try to concatenate a string, it zeros out the destination string first. Am I doing this wrong?

Thanks Sean

Answer 1

I think you'll get closer to what you want by using the right MATLAB Coder directives:

function testStrCat()
  path = coder.nullcopy(char(zeros(1, 40)));
  fspec = coder.nullcopy(char(zeros(1, 132)));
  coder.ceval('strcat', coder.ref(path), ['path' 0]); %null-termination
  coder.ceval('strcat', coder.ref(fspec), path);
  coder.ceval('strcat', coder.ref(fspec), '/');

Now the code looks like:

void testStrCat(void)
{
  char_T path[40];
  char_T fspec[132];
  char_T cv0[5];
  int32_T i0;
  static const char_T cv1[5] = { 'p', 'a', 't', 'h', '\x00' };
    for (i0 = 0; i0 < 5; i0++) {
      cv0[i0] = cv1[i0];
    }
    strcat(path, cv0);
    strcat(fspec, path);
    strcat(fspec, '/');
  }

I don't know how you can avoid that extra copy for the string "path".