objective c: passing a char argument to function crashes the app - iphone

Question

I wrote a singleton called SomeValues where I initialize a foo NSMutableArray. I then tried to write a function SetBFSV to set the values of this array from different control views.
#interface SomeValues : NSObject {
NSMutableArray *foo;}
+ (SomeValues *) sharedInstance;
#implementation
...
- (void) SetBFSV:(char)lbl ToVal:(long)BFSvl{
NSNumber *ValueBFSvl = [NSNumber numberWithLong:BFSvl];
NSString *Strlbl = [[NSString alloc] stringWithFormat:#"%s",lbl];
[foo setValue:ValueBFSvl forKey:Strlbl];
}
I know that setValue requires a NS object for both the value and the key, but I cannot declare my function as
(void) SetBFSV:(NSString)lbl ToVal:(NSNumber)BFSvl
because it doesn't compile with the error: "Can not use an object as parameter to a method".
In one ControlView I wrote then this piece of code:
SomeValues *myBFSV = [SomeValues sharedInstance];
const unsigned char *Bar = (unsigned char *)[#"Label1" UTF8String];
NSLog(#"The string %s", Bar);
[myBFSV SetBFSV:Bar ToVal:2.5];
When compiling I get a warning on the last line:
warning: passing argument 1 of 'SetBFSV:ToVal:' makes integer from pointer without a cast
Which integer? I'm getting stupid looking around for it. When running I get the print out from the NSLog, but right afterwards the program obviously crashes with this error:
'NSInvalidArgumentException', reason: '-[NSPlaceholderString stringWithFormat:]: unrecognized selector sent to instance 0x4e03280'
Clearly I'm passing something wrong to stringWithFormat but I cannot understand what.
Thanks for any help. Have a nice day!
/luca

Answer 1

Possible problems with your code (unless you have typos in it):
- (void) SetBFSV:(char)lbl ToVal:(long)BFSvl function expects char as its 1st parameter but you pass it a char* - your 1st warning probably comes from here
stringWithFormat is a class method so your code should look either:
NSString *Strlbl = [[NSString alloc] initWithFormat:#"%s",lbl];
[foo setValue:ValueBFSvl forKey:Strlbl]
or
NSString *Strlbl = [NSString stringWithFormat:#"%s",lbl];
[foo setValue:ValueBFSvl forKey:Strlbl]
since you try to use -stringWithFormat instead of +stringWithFormat you get a crash
If you pass char to a function then correct format specifier for it will be %c, not %s
You probably must release your Strlbl variable if you create it with alloc/init otherwise it will leak (but you must not release it if you use +stringWithFormat:)

Answer 2

For one, you can't use an object as a paramter:
(void) SetBFSV:(NSString)lbl ToVal:(NSNumber)BFSvl
You need to pass them as pointers, using the asterisk.
(void) SetBFSV:(NSString*)lbl ToVal:(NSNumber*)BFSvl
Furthermore, if you need to pass them as (char) and (long) your bit of code:
SomeValues *myBFSV = [SomeValues sharedInstance];
const unsigned char *Bar = (unsigned char *)[#"Label1" UTF8String];
NSLog(#"The string %s", Bar);
[myBFSV SetBFSV:Bar ToVal:2.5]; // in either case, this is a long. why are you passing a double here?
Passes *Bar as a pointer. You should really read up on the pointers and objects. IF you need to pass them in as (const char*) and (long) do it like this:
- (void) SetBFSV:(const char*)lbl ToVal:(long)BFSvl{
NSNumber *ValueBFSvl = [NSNumber numberWithLong:BFSvl];
NSString *Strlbl = [NSString stringWithUTF8String: lbl]; // your old code had a memory leak here. you need to either create an autorelease object, or release it after adding to `foo`
[foo setValue:ValueBFSvl forKey:Strlbl];
}
My Recommendation is to do the following:
- (void) SetBFSV:(NSString*)key ToVal:(long)val{
NSNumber *value = [NSNumber numberWithLong:val];
[foo setValue:value forKey:key];
}
And call it like the following (from your example):
SomeValues *myBFSV = [SomeValues sharedInstance];
NSString *Bar = [NSString stringWithString:#"Label1"];// this may not be necessary...
NSLog(#"The string %#", Bar);
[myBFSV SetBFSV:Bar ToVal:25]; // don't pass a decimal for a (long)