CODEWITHSUNDEEP
javacpointerscharjava-native-interface
Jas On
Jas On

Reputation: 51

C Pointers - Invalid Conversion from Char to Char*

I'm currently coding a Java application which loads a native library coded in C. A C function which gets called from Java is passed a jchar. In that C function, another library gets loaded with a new function which needs the jchar converted to a char* pointer. All I know about that new function is that it takes a pointer to a char value as parameter (char* parity).

This is my current code:

JNIEXPORT jint JNICALL Java_analyzer_DeclareNative_init (JNIEnv *env, jobject obj, ... , jchar parity, ...) {

    typedef int (__stdcall *Init) (..., char* parity, ...);
    HINSTANCE hinstLib = LoadLibrary("rs232");

    Init initcon = (Init) GetProcAdress(hinstLib, "functionname");

    char p = (char) parity;  //(Typecasting jchar to char)
    char *pchar = &p;  //(Creating a pointer to p)

    initcon(..., *pchar, ...);
}

When I try to compile this code, it throws following error: "Invalid conversion from char to char*"

Upvotes: 0

Views: 201

Answers (3)

bmargulies
bmargulies

Reputation: 100123

jchar is a single 16-bit, UTF-16, Unicode character. '&' of it is not char *, and will not work passed to a char *. You need to convert it to the ACP and null-terminate it. WideCharToMultiByte might prove helpful.

Upvotes: 0

Piotr Wilkin
Piotr Wilkin

Reputation: 3501

As @bmargulies already pointed out, the problem here is that you are not passing pchar (which is of type (char *), but *pchar. * is a dereferencing operator and it means "give me whatever is at the address pointed to by pchar. In other words - a single char.

Upvotes: 2

Alan H.
Alan H.

Reputation: 11

If you look at your function parameters you'll see that parityis coming in as a char *, yet further down you have this line:

char p = (char) parity;

You're casting a char pointer to a char. You don't need to do this based upon what you appear to need on the next line:

char *pchar = &p;

You already have parity as a char * as a result of the parameter being passed in.

Upvotes: 0

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