Warning "Implicit conversion loses integer precision..."

12
votes

I am doing a shopping cart tutorial: I have an array that collects input from a text field, and then displays it in the NSTableView. You can check an item, and remove it from the list. I want to display a warning only if something is checked. So, I have this:

    -(IBAction)removeItemFromShoppingList:(id)sender {
        int selectedItemIndex = [shoppingListTableView selectedRow];
        if (selectedItemIndex == -1) return;
        NSAlert *alert = [[NSAlert alloc] init];
        ...
        [alert runModal];
        [alert release];
}

On line 2 here (int selectedItemIndex...) I get a yellow warning: Implicit conversion loses integer precision:’NSInteger’ (aka ‘long’) to ‘int’.

Why?

7
arrayscocoawarningsnstableview
Maybe because an int is shorter than a long? - Hot Licks
As an aside, you should only see this warning when building for the simulator since NSInteger is 32 bits when building for the device. As others have said, you should use the same precision types or explicitly cast to say "I know for a fact this will never be larger than 32 bytes". - Jason Coco
What do you mean "only building for the simulator"? (It's for a Mac application, not iOS) - janeh
To remove warning: int selectedItemIndex = (int)[shoppingListTableView selectedRow]; - rjobidon

7 Answers

14
votes

From apple's documentation:

When building 32-bit applications, NSInteger is a 32-bit integer. A 64-bit application treats NSInteger as a 64-bit integer.

#if __LP64__ || TARGET_OS_EMBEDDED || TARGET_OS_IPHONE || TARGET_OS_WIN32 || NS_BUILD_32_LIKE_64
typedef long NSInteger;
#else
typedef int NSInteger;
#endif

UPDATE:

Explain in detail:

[shoppingListTableView selectedRow] returns a NSInteger, and you are building an 64-bit application, so it is in fact a long.

You can use long selectedItemIndex instead of int selectedItemIndex to suppress this warning, but the warning appears again when building 32-bit version.

A better way is using NSInteger selectedItemIndex, which handles this case correctly.

8
votes

Because your variable is of type int and you are trying to copy the value of a variable of type NSInteger into it. An NSInteger can hold larger values than an int can, so you get a warning that overflow is possible. Probably the simplest fix is to change int to NSInteger. (When you want to copy the value of a variable to run tests on it, you should usually use a variable of the same type.)

6
votes

Use

int selectedItemIndex = (int)[shoppingListTableView selectedRow];

Instead of

int selectedItemIndex = [shoppingListTableView selectedRow];
2
votes

The selectedRow: method returns a value of type NSInteger.

You should make your selectedItemIndex of type NSInteger.

Please refer to:

http://developer.apple.com/library/mac/ipad/#documentation/Cocoa/Reference/ApplicationKit/Classes/NSTableView_Class/Reference/Reference.html

1
votes

Use

   NSInteger selectedItemIndex = [shoppingListTableView selectedRow];

Instead of

   int selectedItemIndex = [shoppingListTableView selectedRow];
1
votes

You can update project settings, to remove all

Implicit conversion loses integer precision warnings, by setting

Implicit Conversion to 32 Bit Type to No

in project's build settings.

enter image description here

0
votes

I get out warning just do: 

int selectedItemIndex = (int)[shoppingListTableView selectedRow];