Objective-C LanguageFormat-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.