NSMutableArray : getObject method returning null

Question

This program should take 5 NSString's in input and print them. I put them in an NSMutableArray. During the loop if I try to print the NSString's they're printed correctly. But when I try getting the objects from the array, I don't know why it returns null. So if I try printing them in the second loop, they're all null.

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[])
{
    NSAutoreleasePool* pool=[[NSAutoreleasePool alloc]init];
    NSMutableArray* array;
    NSString* str=[[NSString alloc]init];
    char* cstr;
    cstr=(char*)calloc(100,sizeof(char));
    for(int i=0;i<5;i++)
    {
        fgets(cstr,100,stdin);
        str=[NSString stringWithUTF8String:cstr];
        [array addObject : str];
    }
    for(int i=0;i<5;i++)
    {
        str=[array objectAtIndex:i];
        NSLog(@"%@",str);
    }        
    [pool drain];
    return 0;
}

possible duplicate of Why is NSMutableArray showing count size of 0? — JeremyP
– JeremyP, Commented Mar 7, 2012 at 16:38
possible duplicate of Cannot add items to an NSMutableArray ivar — jscs
– jscs, Commented Mar 7, 2012 at 19:52

yuji · Accepted Answer · 2012-03-07 16:04:53Z

2

In this line:

NSMutableArray* array;

You are declaring array, to be an NSMutableArray, but you're not setting the pointer to anything, so array is just nil.

You want to do this instead to allocate and initialize an actual instance of NSMutableArray and assign it to that pointer:

NSMutableArray* array = [[NSMutableArray alloc] init];

answered Mar 7, 2012 at 16:04

yuji

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Aaron Hayman · Accepted Answer · 2012-03-07 16:02:55Z

2

You haven't initialized your array. You should put: NSMutableArray *array = [[NSMutableArray alloc] init];

or better yet: NSMutableArray *array = [[NSMutableArray alloc] initWithCapacity:5];

answered Mar 7, 2012 at 16:02

Aaron Hayman

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