error: incompatible types when assigning to type 'double' from type 'char *' c2_b_y = doble(c2_b_u);

Hello all again;

I want to ask for your help to understand this problem. I need to make a converter from float value to string, to be send by serial transmit of my Tiva C launchpad. Im trying to make the conversion in a simulink function block using the sprintf function.

During the debug in the Code Compiler Studio it works fine.

The problem ocurrs with Matlab, that give this error:

Building with 'MinGW64 Compiler (C)'. 
C:\Users\Alberto\Desktop\slprj\_sfprj\untitled\_self\sfun\src\c2_untitled.c: In function 'sf_gateway_c2_untitled': 
C:\Users\Alberto\Desktop\slprj\_sfprj\untitled\_self\sfun\src\c2_untitled.c:180:10: error: incompatible types when assigning to type 'double' from type 'char *' 
   c2_b_y = doble(c2_b_u); 
          ^ 

gmake: *** [c2_untitled.obj] Error -1
Component: Make | Category: Make error
Unable to create mex function 'untitled_sfun.mexw64' required for simulation.

This is the C code:

#include <stdio.h>
#include "dobloh.h"
double u;
char* doble(double u)
{
    static char car[2000];
    sprintf(car,"%.3f",u);
    return car;
}

"dobloh.h" Header:

#ifndef DOBLADOR_C_
#define DOBLADOR_C_
char* doble(double u);
#endif /* DOBLADOR_C_ */

Function block code:

function y = callingDoblez(u)
%#codegen
y=0.0;
y =  coder.ceval('doble',u);

I hope you can help me to understand the problem,

Thanks for your time

Regards

Alberto

Answer 1

[Venkatachala Sarma]

Hi Alberto,

I think this summarizes all your recent queries :)

So Simulink tries to check if the model is fit for generating code before it actually generates code. To do this, Simulink generates a MEX file for your model and tries to simulate it. 'coder.ceval' is a function which works only for code generation and it has to be excluded from Simulation. So try to use the following code in the MATLAB Function block

 function y = callingDoblez(u)
%#codegen
y=0.0;
if(coder.target('Rtw')
y =  coder.ceval('doble',u);
end
end

This guard coder.target('Rtw') restricts 'coder.ceval' to be visible to simulation and shows it only to code generation.

I hope this resolves the issue.