Assign char*[] to void**

[cmajor28]

So I'm using an old API and it has a problem I don't know how to solve.
It's something like this.

int function(int selector, void **value) {
    
    char *names[32];
    long length = getNames(names); // Returns number of elements, length is used for something else
    
    // HERE IS THE PROBLEM, value does not get any of the names
    value = (void**)names;

    return 0; // Returns error code
}

[csstudent123]

try casting a type to value?

[cmajor28]

What do you mean?

[coder777]

You cannot change the value of a passed parameter (it is a local variable). You can only change the content (if possible of that parameter).

In your case you may pass a reference:

int function(int selector, void **&value) { // Note & in order to change value
    
    char *names[32];
    long length = getNames(names); // Returns number of elements, length is used for something else
    
    // HERE IS THE PROBLEM, value does not get any of the names
    value = (void**)names;

    return 0; // Returns error code
}

[cmajor28]

Oh pass by reference, I see. The casting word threw me off.

[coder777]

One more thing i forgot to mention: You cannot assign the local variable names to the a non local variable (such as value). As soon as function(...) ends the life time of names also ends. The content of value when returning is undefined.

Generally: Do not return pointers to local variables.

So if getNames(...) returns pointers to local variable as well it would be undefined as well.

[cmajor28]

This actually works. Everything is returned correctly. And that void** has the value of everything.

		if (!asioDrivers)
			asioDrivers = new AsioDrivers;

		char *driverNames[MAX_NUMBER_OF_DRIVERS];
		long length = asioDrivers->getDriverNames(driverNames, MAX_NUMBER_OF_DRIVERS);

		for (size_t index = 0; index < MAX_NUMBER_OF_DRIVERS; index++) {
			if (index < length)
				value[index] = driverNames[index];
			else
				value[index] = NULL;
		}
		return true;