Converting NSString to Hex - objective-c

Question

I've been doing a lot of reading on how to convert a string to a hex value. Here is what I found to accomplish this:
NSString * hexString = [NSString stringWithFormat:#"%x", midiValue];
This returned some "interesting" results and upon reading a little further I found a post that mentioned this
"You're passing a pointer to an object representing a numeric value, not the numeric value proper."
So I substituted 192 instead of "midiValue" and it did what I expected.
How would I pass the string value and not the pointer?
Decleration of midiValue:
NSString *dMidiInfo = [object valueForKey:#"midiInformation"];
int midiValue = dMidiInfo;

Answer 1

You probably need to do something like this:
NSNumberFormatter *numberFormatter= [[NSNumberFormatter alloc] init];
int anInt= [[numberFormatter numberFromString:string ] intValue];
also, I think there is some example code in the xcode documentation for converting to and from a hex value, in the QTMetadataEditor sample. in the MyValueFormatter class.
+ (NSString *)hexStringFromData:(NSData*) dataValue{
UInt32 byteLength = [dataValue length], byteCounter = 0;
UInt32 stringLength = (byteLength*2) + 1, stringCounter = 0;
unsigned char dstBuffer[stringLength];
unsigned char srcBuffer[byteLength];
unsigned char *srcPtr = srcBuffer;
[dataValue getBytes:srcBuffer];
const unsigned char t[16] = "0123456789ABCDEF";
for (; byteCounter < byteLength; byteCounter++){
unsigned src = *srcPtr;
dstBuffer[stringCounter++] = t[src>>4];
dstBuffer[stringCounter++] = t[src & 15];
srcPtr++;
}
dstBuffer[stringCounter] = '\0';
return [NSString stringWithUTF8String:(char*)dstBuffer];
}
+ (NSData *)dataFromHexString:(NSString*) dataValue{
UInt32 stringLength = [dataValue length];
UInt32 byteLength = stringLength/2;
UInt32 byteCounter = 0;
unsigned char srcBuffer[stringLength];
[dataValue getCString:(char *)srcBuffer];
unsigned char *srcPtr = srcBuffer;
Byte dstBuffer[byteLength];
Byte *dst = dstBuffer;
for(; byteCounter < byteLength;){
unsigned char c = *srcPtr++;
unsigned char d = *srcPtr++;
unsigned hi = 0, lo = 0;
hi = charTo4Bits(c);
lo = charTo4Bits(d);
if (hi== 255 || lo == 255){
//errorCase
return nil;
}
dstBuffer[byteCounter++] = ((hi << 4) | lo);
}
return [NSData dataWithBytes:dst length:byteLength];
}
Hopefully this helps.

Answer 2

if you are messing with a simple iPhone app in Xcode using the iPhone 5.1 Simulator then this is useful:
//========================================================
// This action is executed whenever the hex button is
// tapped by the user.
//========================================================
- (IBAction)hexPressed:(UIButton *)sender
{
// Change the current base to hex.
self.currentBase = #"hex";
// Aquire string object from text feild and store in a NSString object
NSString *temp = self.labelDisplay.text;
// Cast NSString object into an Int and the using NSString method StringWithFormat
// which is similar to c's printf format then output into hexidecimal then return
// this NSString object with the hexidecimal value back to the text field for display
self.labelDisplay.text=[NSString stringWithFormat:#"%x",[temp intValue]];
}