Hello, I am trying to convert a very simple Matlab program (connect two input strings together) to a C standalone executable using Matlab Coder. The m file I have is: function r = connect(a,b) %#codegen assert(isa(a,'char')); assert(isa(b,'char')); r = [a,b]; The main.c I have is: #include #include #include "connect.h" #include "connect_initialize.h" #include "connect_terminate.h" int main(int argc, char *argv[]) { connect_initialize(); printf("Result is %s\n", connect(argv[1],argv[2])); connect_terminate(); return 0; } The error message I got is: 26 C:\C\connect\main.c(16) : warning C4047: 'function' : 'char_T' differs in levels of indirection from 'char *' 27 C:\C\connect\main.c(16) : warning C4024: 'connect' : different types for formal and actual parameter 1 28 C:\C\connect\main.c(16) : warning C4047: 'function' : 'char_T' differs in levels of indirection from 'char *' 29 C:\C\connect\main.c(16) : warning C4024: 'connect' : different types for formal and actual parameter 2 I'd really appreciate it if somebody can give me a hint. Thanks.

Problem converting Matlab code to C standalone executable using Matlab Coder

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Hank 2012년 9월 3일

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https://kr.mathworks.com/matlabcentral/answers/47231-problem-converting-matlab-code-to-c-standalone-executable-using-matlab-coder

댓글: Prachi Singh 2015년 3월 25일

채택된 답변: Kaustubha Govind

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Hello, I am trying to convert a very simple Matlab program (connect two input strings together) to a C standalone executable using Matlab Coder.

The m file I have is:

function r = connect(a,b) %#codegen
assert(isa(a,'char'));
assert(isa(b,'char'));
r = [a,b];

The main.c I have is:

#include <stdio.h>
#include <stdlib.h>
#include "connect.h"
#include "connect_initialize.h"
#include "connect_terminate.h"
int main(int argc, char *argv[])
{
  connect_initialize();    
  printf("Result is %s\n", connect(argv[1],argv[2]));    
  connect_terminate();    
  return 0;
}

The error message I got is:

 C:\C\connect\main.c(16) : warning C4047: 'function' : 'char_T' differs in levels of indirection from 'char *'
 C:\C\connect\main.c(16) : warning C4024: 'connect' : different types for formal and actual parameter 1
 C:\C\connect\main.c(16) : warning C4047: 'function' : 'char_T' differs in levels of indirection from 'char *'
 C:\C\connect\main.c(16) : warning C4024: 'connect' : different types for formal and actual parameter 2

I'd really appreciate it if somebody can give me a hint. Thanks.

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Hank 2012년 9월 3일

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Hi Walter, thanks for the comment. The connect.h Matlab generated automatically is:

#ifndef __CONNECT_H__
#define __CONNECT_H__
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "rtwtypes.h"
#include "connect_types.h"
extern void connect(char_T a, char_T b, char_T r[2]);
#endif

Did you mean the difference between char* and char_T? I also found this in rtwtypes.h:

typedef char char_T;
typedef char_T byte_T;

This might be the problem, but I don't think I understand C well enough to solve it. Could someone please point me the direction? Thanks.

Prachi Singh 2015년 3월 25일

I am also facing a problem while matlab to c conversion. I am working on ECG Analysis using Pan-Tompkins Algorithm I have a function defined as function [ ecg_m,qrs_amp_raw,qrs_i_raw,delay]= pan_tompkin(ecg,fs,gr) but after converting to c using matlab coder I am getting a function void pan_e(const emxArray_real_T *ecg, real_T fs, real_T gr, emxArray_real_T *ecg_m, real_T *delay)

and there is no a mention of qrs_amp_raw,qrs_i_raw which are mainly needed for further processing. Can someone suggest why this problem is occurring?

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Kaustubha Govind 2012년 9월 4일

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https://kr.mathworks.com/matlabcentral/answers/47231-problem-converting-matlab-code-to-c-standalone-executable-using-matlab-coder#answer_57882

편집: Kaustubha Govind 2012년 9월 4일

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I think you will find this MATLAB Coder demo useful. To be able to pass in a char buffer, I believe you also need to assert on the length:

function r = connect(a,b) %#codegen
assert(isa(a,'char'));
assert(size(a, 1) <= 1024);
assert(isa(b,'char'));
assert(size(b, 1) <= 1024);
r = [a,b];

Note that the generated prototype also expects the length of the strings to be passed in:

extern void myconnect(const char_T a_data[1024], const int32_T a_size[1], const char_T b_data[1024], const int32_T b_size[1], char_T r_data[2048], int32_T r_size[2]);

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Walter Roberson 2012년 9월 7일

Well that's a pain! No input functions at all, and the only output function is disp(). You are probably going to have to use coder.ceval()

Hank 2012년 9월 8일

Yeah, luckily disp() is sufficient for output, but it seems I will have to write some code for input conversion.

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Walter Roberson 2012년 9월 3일

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이 답변에 대한 바로 가기 링크

https://kr.mathworks.com/matlabcentral/answers/47231-problem-converting-matlab-code-to-c-standalone-executable-using-matlab-coder#answer_57723

That C function signature corresponds to passing a single character to "a" and a single character to "b" and (I think) passing in a pointer to an array of exactly 2 characters to write "r" into.

Note: C expects "strings" to be null terminated, and so a C string with 2 usable characters would need 3 positions, the third for the 0 that terminates it. But it is not an error to construct a character array with only exactly 2 non-zero characters, as long as you do not treat it as a string. But in that code, you do try to treat it as a string, as you want to pass the result directly to printf(). One problem with that -- the function does not return anything and instead writes into an address you pass in in the third parameter.

I do not know why the code is expecting single characters instead of character arrays -- the assert() you are using would normally be suitable for character arrays. You probably need to do something different to alert codegen that you are not working with scalars. I speculate that you will need to initialize r to an array that is the maximum size of the string you will return.

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Walter Roberson 2012년 9월 3일

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Those strcpy() will not help. argv[1] and argv[2] are going to be pointers to C strings (null-terminated array of characters). Copying them won't make them any more valid. Copying only part of them might be useful in some cases, but if you were copying only part of them then you would use strncpy() instead of strcpy().

connect() shows up in the .h file as void, meaning it does not return anything. You cannot pass the result of connect() to anything. Instead you have to pass in the address of an array that will receive the result. You can then pass the address of the array into printf(). When you are sizing the array remember to take into account the terminating null that printf() will need. You can do that by passing connect() an array one longer than the maximum result it will write, and writing 0 into the final position after the call returns; or you can pass connect() an array exactly the right size, and then use strncpy() to copy it into a space one larger (and write 0 into the final position.)

To initialize r to the maximum size inside connect, experiment with

r = repmat(' ', 1, 20); %adjust the 20 to your needs

before you do the r = [a,b]

Hank 2012년 9월 4일

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assert(isa(a(10),'char'));

does not seem to be acceptable as Matlab throws a "Preconditioning: No class precondition specified for input 'a' of function 'connect'."

However, after I specify a fourth argument in connect, Matlab actually generated an exe, but when running it in command line, the result just does not make sense, for whatever inputs, it just gives something like "X^" or "Xd" alike.

Here are the latest main.c, connect.m and connect.h:

main.c:

#define Result_Size 40
char string_c[Result_Size];
int sizeArray[] = {1,20};
int main(int argc, char *argv[])
{   
  connect_initialize();
  connect(argv[1], argv[2], string_c, sizeArray);
  string_c[Result_Size - 1] = 0; 
  printf("string_a is %s, string_b is %s, string_c is %s\n", argv[1], argv[2], string_c);
  connect_terminate();    
  return 0;
}

connect.m:

function r = connect(a,b) %#codegen
r = repmat('', 1, 20);
assert(isa(a,'char'));
assert(isa(b,'char'));
r = [a,b];

connect.h:

extern void connect(char_T a, char_T b, char_T r_data[2], int32_T r_sizes[2]);

Really appreciate your patience with me :)

Walter Roberson 2012년 9월 4일

It appears that the following is relevant: http://www.mathworks.com/help/toolbox/eml/ug/br_jxhp.html

Hank 2012년 9월 7일

Thanks again Walter. I wish I could accept two answers. Your answers helped a lot on the C side.

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