(matlab coder)Generating C++ code for scalar string results in a garbled last character?

my entry-point codegen function:

function out = useImageAndString(imagePathstr)%#codegen

arguments
    imagePathstr (1,1) string = "./input.txt" 
end

% https://www.mathworks.com/help/coder/ug/define-input-properties-programmatically-in-the-matlab-file.html
assert(isstring(imagePathstr));
assert(numel(imagePathstr)==1);

% include external C++ functions 
coder.cinclude('test1.h');
coder.updateBuildInfo('addSourceFiles', 'test1.cpp');

% call C++ function 
imgPath = char(imagePathstr); % Must convert to char type to pass to coder.ref/coder.rref ???
coder.ceval('myFunction',coder.rref(imgPath));

end

Generate C++ code for the above function in command line:

s = "./input.txt";
t = coder.typeof(s);
t.StringLength = 255;
t.VariableStringLength = true;
codegen -config:mex useImageAndString -args {t} -launchreport -lang:c++

I can generate C++ code successfully, but the first parameter "imagePathstr" passed to my C++ occasionally results(const char* imagePathstr) in a garbled last character. So how can I fix it?

test1.cpp:

void myFunction(const char* imagePathstr)
{
    std::string dbFile(imagePathstr);
    std::cout << "database name:" << dbFile << std::endl;// The last character is garbled ???
    
    ... do something
}

RUN in R2022b

[xingxingcui]

for example,when i input imagePathstr "../data/preSavedData/database.yml.gz", then pass to myFunction as follows,last character is garbled!

../data/preSavedData/database.yml.gz�

[xingxingcui]

But when I use the relative current ". /" paths or absolute paths, the last characters are not garbled, which is strange！

• "./../data/preSavedData/database.yml.gz"
• "C:/temp/data/preSavedData/database.yml.gz"

These two approaches work！

[Walter Roberson]

I would be interested to know what the binary value is of the character inserted.

[Walter Roberson]

I wonder if it is simply passing the array of bytes without null-padding it? You might need to specifically put on the null, possibly.

[xingxingcui]

@Walter Roberson Unfortunately, this time I went to the last time parent folder and used ". /" relative path instead of using ".. /" in subfolder and still got an error and this is the result of the printed string（last two character）

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I'm also guessing null or "\0" or some such terminator, but what is the exact measure of how to do this? Where does the code need to be changed? How do I change it? thanks for your help again!

-----

During time, I tried to print characters like this：

const char *mystr = NULL;
  //std::string myTT(mystr);
const char charNULL = '\0';

char charBinary = '0';

printf("charNULL:%d,%c,%x,%x \n", charNULL, charNULL, charNULL, mystr);

output:

charNULL:0, ,0,0

Answer 1

[Walter Roberson]

That's probably a NUL character, binary 0 ,

You should test it to see what the binary value is.

[xingxingcui]

@Walter Roberson

I initially thought the same thing, there is a "\0" character at the end of the string in C, but I don't know how to verify if it is "\0" or NULL, what is the practical approach?

Unfortunately, this time I used ". /" relative paths and still got an error（see above comment）

[Walter Roberson]

imgPath = [char(imagePathstr), 0];

[xingxingcui]

@Walter Roberson

Thank you very much, I tried multiple paths and it worked, you can refine your answer so I can accept it