Question

wonder whether someone can help me with the following one…

I have a struct

typedef struct {
    NSString *section;
    NSString *row;
} myStructDef;

that I fill and write from function parameters “value[x]” to an NSMutableArray iVar “Arr1” of NSMUtableArrays local “Arr2” using:

myStruct.section = [NSString stringWithUTF8String:(char *)values[0]];
for (int i=1; i < count; i++) {
    myStruct.row = [NSString stringWithUTF8String:(char *)values[i]];
    [Arr2 addObject:[NSValue valueWithBytes:&myStruct objCType:@encode(myStructDef)]];
    [Arr1 addObject:Arr2];
}

Writing the array seems to work fine (the debugger shows the array building and I can retrieve the NSValue correctly using

[[Arr2 objectAtIndex:i-1] getValue:&myStruct];

added to the for-loop above.

THE PROBLEM comes when retrieving the array values in a subsequent function using:

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section {
    myStructDef myStruct;
    [[[Arr1 objectAtIndex:section] objectAtIndex:0] getValue:&myStruct];
    return myStruct.section;
}

Whilst step1 “[Arr1 objectAtIndex:section]” is retrieved correctly, step3 “… getValue:&myStruct]” seems to fail.
I also tried stripping the 3 actions into separate steps, that is when I can see that an Object is returned in step2. The getValue: fails.

Any clue what i am doing wrong?

cheers
iFloh 🙂

Answer 1

[NSString stringWithUTF8String:] returns a string that you don’t own. You aren’t explicitly retaining it, and a C struct won’t implicitly retain it, either. So you stick your NSString pointers into your array, but the strings they point to are almost certainly deallocated by the time you’re trying to pull them back out.