CODEWITHSUNDEEP
swiftstring
KawaiKx
KawaiKx

Reputation: 9920

How String Comparison happens in Swift

in this example:

var str1 = "hello"
var str2 = "Hello"

if str1 < str2 { print("hello is less than Hello")}
else {print("hello is more than Hello")}

on what basis it is found that str1 is greater than str2?

Upvotes: 8

Views: 7186

Answers (4)

Harsh
Harsh

Reputation: 2908

I think it is based on the Lexicographical Order of the strings.

Upvotes: 0

Aman Sharma
Aman Sharma

Reputation: 1

In Swift 4.2 - //Unicode Value gives you an idea why "hello" is greater than "Hello" as the length of both Strings are the same.

var str1 = "hello"
var str2 = "Hello"

if (str1 < str2){
    print("hello is less than Hello")
}
else {
    print("hello is more than Hello")
}

print(str1.unicodeScalars[str1.unicodeScalars.startIndex].value)
print(str2.unicodeScalars[str2.unicodeScalars.startIndex].value)

Upvotes: 0

Martin R
Martin R

Reputation: 539775

Swift strings are compared according to the Unicode Collation Algorithm, which means that (effectively),

In your example, "hello" and "Hello" have the Unicode values

hello: U+0068, U+0065, U+006C, U+006C, U+006F 
Hello: U+0048, U+0065, U+006C, U+006C, U+006F

and therefore "Hello" < "hello".

The "normalization" or "decomposing" is relevant e.g. for characters with diacritical marks. As an example, 

a = U+0061
ä = U+00E4
b = U+0062

have the decomposed form

a: U+0061
ä: U+0061, U+0308  // LATIN SMALL LETTER A + COMBINING DIAERESIS
b: U+0062

and therefore "a" < "ä" < "b".

For more details and examples, see What does it mean that string and character comparisons in Swift are not locale-sensitive?

Upvotes: 12

rmaddy
rmaddy

Reputation: 318814

The two strings are compared, character by character, using each character's Unicode value. Since h has a higher code (U+0068) than H (U+0048), str1 is "greater" than str2.

Based on Martin's comment below the question, it's slightly more complex than I stated. Please see What does it mean that string and character comparisons in Swift are not locale-sensitive? for more detail.

Upvotes: 8

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