Format-Specifiers

Introduction

Format-Specifiers are used in Objective-c to implant object-values into a string.

Syntax

• %@ //String
• %d //Signed 32-bit integer
• %D //Signed 32-bit integer
• %u //Unsigned 32-bit integer
• %U //Unsigned 32-bit integer
• %x //Unsigned 32-bit integer in lowercase hexadecimal format
• %X //Unsigned 32-bit integer in UPPERCASE hexadecimal format
• %o //Unsigned 32-bit integer in octal format
• %O //Unsigned 32-bit integer in octal format
• %f //64-bit floating-point number
• %F //64-bit floating-point number printed in decimal notation
• %e //64-bit floating-point number in lowercase scientific notation format
• %E //64-bit floating-point number in UPPERCASE scientific notation format
• %g //special case %e which uses %f when less than 4 sig-figs are available, else %e
• %G //special case %E which uses %f when less than 4 sig-figs are available, else %E
• %c //8-bit unsigned character
• %C //16-bit UTF-16 code unit
• %s //UTF8 String
• %S //16-bit variant of %s
• %p //Void Pointer in lowercase hexidecmial format with leading ‘0x’
• %zx //special case %p which removes leading ‘0x’ (For use with no-type cast)
• %a //64-bit floating-point number in scientific notation with leading ‘0x’ and one hexadecimal digit before the decimal point using a ‘p’ to notate the exponent.
• %A //64-bit floating-point number in scientific notation with leading ‘0x’ and one hexadecimal digit before the decimal point using an ‘P’ to notate the exponent.

Remarks

Due to the nature of format-specifiers, if you wish to include the percentage symbol (%) in your string, you must escape it using a second percentage symbol.

Example:

int progress = 45;//percent
NSString *progressString = [NSString stringWithFormat:@"Progress: %i%%", (int)progress];

NSLog(progressString);//logs "Progress: 45%"

No Format Specifier for BOOL-type exists.

Common-use solutions include:

BOOL myBool = YES;
NSString *boolState = [NSString stringWithFormat:@"BOOL state: %@", myBool?@"true":@"false"];

NSLog(boolState);//logs "true"

Which utilizes a ternary operator for casting a string-equivalent.

BOOL myBool = YES;
NSString *boolState = [NSString stringWithFormat:@"BOOL state: %i", myBool];

NSLog(boolState);//logs "1" (binary)

Which utilizes an (int) cast for implanting a binary-equivalent.