C-formatting in Swift

Posted 2022-12-11 chunngai

C-formatting in Swift is similar to that in C: create a String type variable or constant with a c-formatting string, and display the variable or constant using the print() function.

let integerValue: Int = 1
let doubleValue: Double = 2.33
let characterValue: Character = "c"
let stringValue: String = "str"
let boolValue: Bool = true

let characterValueStr = String(characterValue) // (1) Character -> String

let stringToPrint = String(format: "%d %.2f %@ %@", integerValue, doubleValue, characterValueStr, stringValue)
print(stringToPrint)

result:

1 2.33 c str

Something to notice:
A Bool type value cannot be printed with "%b".

A Character type value cannot be printed with "%c". To print a Character type value, convert it into a String type value using the String() initializer, see (1) above.

A String type value can be printed with "%@", not "%s".

Actually we can use the string interpolation in Swift together with the c-formatting, which also enables us to display the Character and Bool type value easily.

let doubleValueStr = String(format: "%.2f", doubleValue)
print("\\(integerValue) \\(doubleValueStr) \\(characterValue) \\(stringValue) \\(boolValue)")

result:

1 2.33 c str true

references:
(1) Swift:字符串格式化
(2) Swift - 数字格式化转成字符串（保留两位小数）
(3) 输出格式化