Question

Basically, my problem is a signed char to int and string conversion in cocoa.

I found this piece of code in an open source cocoa bluetooth application and am trying to apply it to my own.

Basically, I get a signed char output from the variable “RSSI”, and want to convert it to an int and a string, the string for outputting to the log and the int for further calculation. However, no matter what I try, I cannot seem to get it converted, and just get an EXEC_BAD_ACCESS if I try outputting the signed char to the log as it is.

A typical value for the signed char would be ” -57 ‘\307’ ” quoted directly from the process before it is held up by the NSLog. Here’s the code:

- (BOOL)isInRange {
    BluetoothHCIRSSIValue RSSI = 127; /* Valid Range: -127 to +20 */

    if (device) {
        if (![device isConnected]) {
            [device openConnection];
        }
        if ([device isConnected]) {
            RSSI = [device rawRSSI];
            [device closeConnection];
            NSLog(RSSI);
        }
    }
    return (RSSI >= -60 && RSSI <= 20);
}

Thanks in advance.

Answer 1

NSLog() takes an NSString format string as its first argument, and an (optional) variable length list of variables for the format specifiers in the format string after that:

NSLog(@"RSSI: %c", RSSI);

What you’ve got now (NSLog(RSSI);) is simply wrong. It should be giving you compiler warnings like these:

warning: passing argument 1 of 'NSLog' makes pointer from integer without a cast
warning: format not a string literal and no format arguments

You should always pay attention to compiler warnings, not ignore them. Especially when your program crashes on the same line the warnings refer to, they should be a red flag to you that you’ve made a mistake.

As an aside, I should mention that NSLog() works very much like printf(). The two major differences are that NSLog‘s format string should be an Objective-C string literal (@"string"), not a standard C char string ("string"), and that the format specifier for an object is %@. %@ is replaced by the string returned by calling the -description method on the object to be printed.