Implicit declaration of function "..." is invalid in C99?

Question

I'm trying to declare a function within another function. So here's part of my code: ViewController.m

- (void)updatedisplay{
    [_displayText setText:[NSString stringWithFormat:@"%d", counter]];

}

- (IBAction)minus1:(id)sender {
    counter--;
    updatedisplay();
}

ViewController.h

- (IBAction)minus1:(id)sender;
- (void)updatedisplay;

Which returned me the error of "Implicit declaration of function "..." is invalid in C99".

Result: https://i.stack.imgur.com/XGevK.png

I've found that people have encountered similar problem, but as a newbie I didn't really know what to do next. Thanks for your help! :)

Implicit declaration of function '...' is invalid on C99

first learn some basic things related to objective see after that you can implement programs..http://cocoadevcentral.com/d/learn_objectivec/ — Balu, Jul 22 '13 at 05:19

score 14 · Accepted Answer · edited Jul 22 '13 at 05:38

14

You are not declaring a function; but a instance method, so to call it you must send it as a message to self;

[self updatedisplay];

EDIT

As @rmaddy pointed out (thanks for that) it is declared as instance method not class method. To make the things clear;

- (return_type)instance_method_name.... is called via 'self' or pointer to object instance.
+ (return_type)class_method_name.... is called directly on the class (static).

edited Jul 22 '13 at 05:38

iPatel

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answered Jul 22 '13 at 05:14

ludesign

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1

`updatedisplay` is declared as an instance method, not a class method. – rmaddy Jul 22 '13 at 05:17
should I still use 'self' even if the function has parameters? like gettimeofday(&endTime, NULL); – acecapades Oct 30 '13 at 02:30

score 7 · Answer 2 · answered Jul 22 '13 at 05:14

7

Problem

updatedisplay();

solution

[self updatedisplay];

cause

- (void)updatedisplay;

is a class method available for that class.So you have to call from the class to have the method available for you.

answered Jul 22 '13 at 05:14

Lithu T.V

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score 4 · Answer 3 · answered Jul 22 '13 at 05:15

4

That is because you defined your function as a instance method, not a function.

So use it like

- (IBAction)minus1:(id)sender {
    counter--;
    [self updatedisplay]; // Change this line
}

answered Jul 22 '13 at 05:15

βhargavḯ

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score 2 · Answer 4 · answered Jul 22 '13 at 05:14

2

write this way :

[self updatedisplay];

answered Jul 22 '13 at 05:14

KDeogharkar

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Implicit declaration of function "..." is invalid in C99?

4 Answers4