Objective C: Why am I getting "EXC_BAD_ACCESS"?

Question

I'm really new to Objective C and am trying to write a program to go through the collatz conjecture. When I run the program, it stops after the first scanf and comes up with "EXC_BAD_ACCESS". Here's my code:

int original,i;

NSString *PrintFull;

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    NSLog(@"Collatz Conjecture:");
    NSLog(@"Print full results?");
    scanf("%s",PrintFull);

    NSLog(@"What number should we go up to?");
    scanf("%d", &original);

    while (original <= 100) {
        NSLog(@"\n\n%d", original);
        i = original;
        while (i != 1) {
            if (i % 2) {
                i = (i*3)+1;
            } else {
                i = (i/2);
            }

            if ([PrintFull isEqualToString:@"yes"]) {
                NSLog(@"%d",i);
            }
        }

        original++;
    }
}

What am I doing wrong here?

score 2 · Answer 1 · edited May 23 '17 at 11:48

2

scanf does not work with with object types such as NSString. Please see SO post - Using scanf with NSStrings.

edited May 23 '17 at 11:48

Community

1
1

answered Dec 28 '11 at 16:19

5StringRyan

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score 2 · Answer 2 · answered Dec 28 '11 at 16:28

scanf's arguments after the format string should point to already allocated objects. In this case you've just declared a pointer and passed it in without setting it. scanf will try to write to this location, but since the pointer contains a garbage value, the application crashes.
scanf is from the C library 'stdio.h', meaning it doesn't know about NSStrings, which are from the Objective-C 'Foundation' framework.

The following should solve these problems

int original,i;

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    NSLog(@"Collatz Conjecture:");

    NSLog(@"Print full results?");

    char inputBuffer[80];
    scanf("%s", inputBuffer);
    NSString *printFull = [NSString stringWithCString:inputBuffer encoding:NSUTF8Encoding];

It's actually still possible to crash here by typing more than 80 characters. Using `scanf("%80s", inputBuffer);` would prevent this. — joerick, Dec 28 '11 at 16:30

score 1 · Answer 3 · answered Dec 28 '11 at 16:20

1

First, you have to initialize and alloc the NSString. Second, scanf can't handle NSString.

Also notice, that class names begin with a capital letter and class instances with a small one.

answered Dec 28 '11 at 16:20

tamasgal

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Objective C: Why am I getting "EXC_BAD_ACCESS"?

3 Answers3