Understanding NSString comparison

Question

Both the following comparisons evaluate to true:

1)

@\"foo\" == @\"foo\";

2)

NSString *myString1 = @\"foo\";
NSStri         


        

Answer 1

The equality operator == only compares pointer addresses. When you create two identical strings using the literal @"" syntax, the compiler will detect that they are equal, and only store the data once. Hence, the two pointers point to the same location. However, strings created by other means may contain identical data, yet be stored at different memory locations. Hence, you should always use isEqual: when comparing strings.

Note that isEqual: and isEqualToString: always return the same value, but isEqualToString: is faster.