NSInteger returning 0 if NSString is NULL

Question

This could be the simplest one but I am not able to find the exact cause. Instead to explain in words following is my code:

NSString *str = @"";
NSInteger tempInteger = [str integerValue];

if (tempInteger == 0)
{
  NSLog (@"do something");
}

If NSString returning NULL then NSInteger returning 0 and if NSStringhas some value then NSInteger returning same value.

But when NSString is NULL then I want NSInteger should return NULL not 0 but I am not able to validation NSInteger as NULL.

How can I get NULL value in NSInteger if NSString is NULL?

Answer 1

NULL is a pointer; NSInteger is a C primitive that can only hold numbers. It is not possible for an NSInteger to ever be NULL. (Sidenote: when we speak of Objective-C object pointers, we use nil rather than NULL.)

Instead, if you wish to handle only cases where the integer value is 0, but the string is not NULL, you should change your condition as follows:

if (tempInteger == 0 && str != nil)

However, in your case, the string is not nil; it is merely an existent--but empty--string. If you wish to also check for that, your condition could become:

if (tempInteger == 0 && [str length] > 0)

This checks both cases because a nil string will return length 0. (In fact, any method sent to nil will return 0, nil, 0.0, etc. depending on the return type.)

Answer 2

Actually you could implement a logic such as this:

1. Check if your string is indeed an integer
2. Try to convert it
3. If it's equal to 0 do something

Something like this would do the trick:

NSString *str = @"";
NSInteger tempInteger = [str integerValue];
NSCharacterSet *cs = [NSCharacterSet decimalDigitCharacterSet];
BOOL safe = [cs isSupersetOfSet:[NSCharacterSet characterSetWithCharactersInString:str]] && str.length > 0;

if (safe && tempInteger == 0)
{
  NSLog (@"do something");
}

Answer 3

An integer can only hold numbers an nut null value. In this case you should first check the length of string to check if it's null

Answer 4

NSInteger is a scalar variable type. The value NULL (actually nil in ObjectiveC), indicating a pointer towards the address 0, when cast to an NSInteger will be 0.

For accomplishing your task, you will have to compare NSString against nil before converting it towards an integer.

if (str == nil)
{
   //our string is invalid
}
else
{
    tempInteger = [str integerValue];
}