Problem with implicit declaration of function in objective c

Question

I trying to learn a bit more about Objective-c, and at the moment i'm stuck. I got 4 errors, all the same. "Implicit declaration of function", I googled it but i didn't find a solution.

RadioStation .h

#import <Cocoa/Cocoa.h>
@interface RadioStation : NSObject {
  NSString* name;
  double frequency;
  char band;
}
+(double)minAMFrequency;
+(double)maxAMFrequency;
+(double)minFMFrequency;
+(double)maxFMFrequency;
-(id)initWithName:(NSString*)newName atFrequency:(double)newFrequency withBand:(char)newBand;
-(NSString*)name;
-(double)frequency;
-(char)band;
-(void)setName:(NSString*)newName;
-(void)setFrequency:(double)newFrequency;
-(void)setBand:(char)newBand;
@end

RadioStation .m

#import "RadioStation.h"

@implementation RadioStation
+(double)minAMFrequency{
 return 520.0;
};
+(double)maxAMFrequency{
     return 1610.0;
};
+(double)minFMFrequency{
 return 88.3;
};
+(double)maxFMFrequency{
 return 107.9;
};
-(id)initWithName:(NSString*)newName atFrequency:(double)newFrequency withBand:(char)newBand{
 self = [super init];
 if(self != nil){
  name = [newName retain];
  band = newBand;
  if (band == 'F') {
   if (newFrequency > maxFMFrequency()) {
    frequency = maxFMFrequency();
   }else if (newFrequency < minFMFrequency()) {
    frequency = minFMFrequency();
   }else {
    frequency = newFrequency;
   }

  }else if (band == 'A') {
   if (newFrequency > maxAMFrequency()) {
    frequency = maxAMFrequency();
   }else if (newFrequency < minAMFrequency()) {
    frequency = minAMFrequency();
   }else {
    frequency = newFrequency;
   }
  }
 }
 return self;
}
@end

The lines

if (newFrequency > maxFMFrequency()) {
if (newFrequency < minFMFrequency()) {
if (newFrequency > maxAMFrequency()) {
if (newFrequency < minAMFrequency()) {

all say "Implicit declaration of function"

Thanx in advance, Dietger

theChrisKent · Accepted Answer · 2011-01-25 15:18:03Z

9

These are class methods so you will need to change each of them as follows:

if (newFrequency > [RadioStation maxFMFrequency]) {
if (newFrequency < [RadioStation minFMFrequency]) {
if (newFrequency > [RadioStation maxAMFrequency]) {
if (newFrequency < [RadioStation minAMFrequency]) {

edited Jan 25, 2011 at 15:18

answered Jan 25, 2011 at 14:14

theChrisKent

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5 Comments

Madi Over a year ago

Thx, this was the solution for my prolem

Dave Over a year ago

Would the correct wording be "class methods" rather than "instance methods"?

theChrisKent Over a year ago

@Dave, yip! I saw that I wrote static and "corrected" it without thinking, whoops. Good catch, thanks.

Richard Over a year ago

probably better to use [[self class] maxFMFrequency] etc. in case a subclass would override the class methods to return different constants.

apanloco Over a year ago

Please mark this answer as the correct one. Or at least one that is correct.

mmmmmm · Accepted Answer · 2011-01-25 14:14:41Z

3

You are mixing up methods and functions.

the code you call the thing with

if (newFrequency > maxFMFrequency()) {

expects to see a declaration of a function like

double maxFMFrequency()

implemented as a C function - this will not be able to get data from the object so you need to use a methof

the header does declare a method as

+(double)maxFMFrequency;

but needs to be called as

if (newFrequency > [RadioStation maxFMFrequency])

answered Jan 25, 2011 at 14:14

mmmmmm

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Comments

Dave · Accepted Answer · 2011-01-25 14:12:43Z

2

I think it might be because you're mixing C and Objective C syntax.

Try:

if (newFrequency > [self maxFMFrequency])

answered Jan 25, 2011 at 14:12

Dave

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3 Comments

Madi Over a year ago

this returned an invalid operands to binary >

Dave Over a year ago

Hmm... Perhaps Mark or theChris could enlighten us as to why. It'll be worth a vote-up from me!

theChrisKent Over a year ago

the problem is that when you access the method as if it were an instance method as you are doing above, it returns a pointer and the compiler assumes you want to do a binary operation on it. > is not a binary operator so it throws that error. I appreciate your effort, but this answer is NOT correct as stated by the OP in the comment above so not sure why it was picked. Must be your lucky day! :)

paulb · Accepted Answer · 2011-10-19 17:33:07Z

1

I faced same problem. sorted by modifying the function call as given below

//function declaration 
-(void) downloadPage:(NSString *)url;

//function definition 
-(void) downloadPage:(NSString *)url
{
userOutput.text = url;
}

//and now the fixed call to downloadPage

-(IBAction) onButtonOneClicked:(id) sender
{
userOutput.text = @"please wait...";
    //fixed call to downloadPage
[self downloadPage:[userInput text]];
}

answered Oct 19, 2011 at 17:33

paulb

111 bronze badge

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