Calllib with C++ out char *parameter

Hello,

I'm doing an example of my sdk. The c++ function on header is

int myfunction(int index, out char *parameter);

So my call in MATLAB is

strOutParameter = "00";
[intReturned, strOutParameter] = calllib('myLib', 'myfunction', index, strOutParamter);

I use this reference for the types mathworks.com/help/matlab/matlab_external/matlab-to-c-data-type-mapping.html

I try it but it isn't working. I've an error :

Error using calllib
Parameter can not be converted to a character vector

I really don't code on MATLAB. I'm just doing a little example file of few lines for my users.

So my question is ; How to pass and get a out char * parameter ?

Thanks in advance

Answer 1

[Rishav]

Hi Justin,

In MATLAB, when passing and receiving char* parameters to and from C++ functions using 'calllib' function, you need to handle them as MATLAB strings (char arrays).

Here is how you can modify your MATLAB code:

% Define the input parameters
index = 1;
strOutParameter = blanks(256);

% Call the C++ function using calllib
[intReturned, strOutParameter] = calllib('myLib', 'myfunction', index, strOutParameter);

% Convert the output parameter to a string
strOutParameter = strtrim(strOutParameter); 

where,

• blanks(256) return 1-by-n array of space characters.
• strtrim is used to remove any trailing whitespace characters from the output parameter.

Please refer to the below documentations for more details on:

1. blanks: https://www.mathworks.com/help/matlab/ref/blanks.html
2. strtrim: https://www.mathworks.com/help/matlab/ref/strtrim.html