Converting string from C++ to Swift

December 5, 2021

I am trying to use C++ functions in Swift. To do that I use Objective-C wrapper. I am not familiar with Objective-C and C++ so much.

My Wrapper function takes Swift String as a parameter from textField.
And inside of c++ I encrypt the passed string and return it.

Here is my Cpp function:

string StringModifier::encryptString(string str) {
    int i;
    for(i=0; (i<100 && str[i] != '\n'); i++) {
        str[i] = str[i] + 2;
    }
    return str;
}

And inside of Wrapper

StringModifier stringModifier;

-(NSString*)encryptString:(NSString*)str; {
    string strng = [str UTF8String];
    string finalString = stringModifier.encryptString(strng);
    NSString *result = [NSString stringWithCString: finalString.c_str() encoding:[NSString defaultCStringEncoding]];
    return result;
    
}

The output of encryptString("Helloworld") is "Jgnnqyqtnf¬√√0*?"
and after couple of calling this method throws EXC_BAD_ACCESS error.

How can I solve this problem?

Thanks.

>Solution :

You need to check for the null character (\0) in C++.

Change your for-loop to this:

for(i=0; (i<100 && str[i] != '\n' && str[i] != '\0'); i++) {
    str[i] = str[i] + 2;
}

Even better, loop depending on how big the string is:

string StringModifier::encryptString(string str) {
    for (int i = 0; i < str.size() && str[i] != '\n'; i++) {
        str[i] = str[i] + 2;
    }
    return str;
}