Table 1  Format specifiers supported by the NSString formatting methods and CFString formatting functions
Specifier Description
%@ Objective-C object, printed as the string returned by descriptionWithLocale: if available, or description otherwise. Also works with CFTypeRef objects, returning the result of the CFCopyDescription function.
%% '%' character
%d%D,%i Signed 32-bit integer (int)
%u%U Unsigned 32-bit integer (unsigned int)
%hi Signed 16-bit integer (short)
%hu Unsigned 16-bit integer (unsigned short)
%qi Signed 64-bit integer (long long)
%qu Unsigned 64-bit integer (unsigned long long)
%x Unsigned 32-bit integer (unsigned int), printed in hexadecimal using the digits 0–9 and lowercase a–f
%X Unsigned 32-bit integer (unsigned int), printed in hexadecimal using the digits 0–9 and uppercase A–F
%qx Unsigned 64-bit integer (unsigned long long), printed in hexadecimal using the digits 0–9 and lowercase a–f
%qX Unsigned 64-bit integer (unsigned long long), printed in hexadecimal using the digits 0–9 and uppercase A–F
%o%O Unsigned 32-bit integer (unsigned int), printed in octal
%f 64-bit floating-point number (double)
%e 64-bit floating-point number (double), printed in scientific notation using a lowercase e to introduce the exponent
%E 64-bit floating-point number (double), printed in scientific notation using an uppercase E to introduce the exponent
%g 64-bit floating-point number (double), printed in the style of %e if the exponent is less than –4 or greater than or equal to the precision, in the style of %f otherwise
%G 64-bit floating-point number (double), printed in the style of %E if the exponent is less than –4 or greater than or equal to the precision, in the style of %f otherwise
%c 8-bit unsigned character (unsigned char), printed by NSLog() as an ASCII character, or, if not an ASCII character, in the octal format \ddd or the Unicode hexadecimal format \udddd, where d is a digit
%C 16-bit Unicode character (unichar), printed by NSLog() as an ASCII character, or, if not an ASCII character, in the octal format \ddd or the Unicode hexadecimal format \udddd, where d is a digit
%s Null-terminated array of 8-bit unsigned characters. %s interprets its input in the system encoding rather than, for example, UTF-8.
%S Null-terminated array of 16-bit Unicode characters
%p Void pointer (void *), printed in hexadecimal with the digits 0–9 and lowercase a–f, with a leading 0x
%L Length modifier specifying that a following aAeEfFg, or G conversion specifier applies to a long double argument
%a 64-bit floating-point number (double), printed in scientific notation with a leading 0x and one hexadecimal digit before the decimal point using a lowercase p to introduce the exponent
%A 64-bit floating-point number (double), printed in scientific notation with a leading 0X and one hexadecimal digit before the decimal point using a uppercase P to introduce the exponent
%F 64-bit floating-point number (double), printed in decimal notation
%z Length modifier specifying that a following dioux, or X conversion specifier applies to a size_t or the corresponding signed integer type argument
%t Length modifier specifying that a following dioux, or X conversion specifier applies to a ptrdiff_t or the corresponding unsigned integer type argument
%j Length modifier specifying that a following dioux, or X conversion specifier applies to a intmax_t or uintmax_t argument

Platform Dependencies

Mac OS X uses several data types—NSIntegerNSUInteger,CGFloat, and CFIndex—to provide a consistent means of representing values in 32- and 64-bit environments. In a 32-bit environment, NSInteger and NSUInteger are defined as int and unsigned int, respectively. In 64-bit environments, NSInteger and NSUInteger are defined as longand unsigned long, respectively. To avoid the need to use different printf-style type specifiers depending on the platform, you can use the specifiers shown in Table 2. Note that in some cases you may have to cast the value.

Table 2  Format specifiers for data types
Type Format specifier Considerations
NSInteger %ld or %lx Cast the value to long
NSUInteger %lu or %lx Cast the value to unsigned long
CGFloat %f or %g %f works for floats and doubles when formatting; but see below warning when scanning
CFIndex %ld or %lx The same as NSInteger
pointer %p %p adds 0x to the beginning of the output. If you don’t want that, use %lx and cast to long.
long long %lld or %llx long long is 64-bit on both 32- and 64-bit platforms
unsigned long long %llu or %llx unsigned long long is 64-bit on both 32- and 64-bit platforms

The following example illustrates the use of %ld to format an NSInteger and the use of a cast.

NSInteger i = 42;
printf("%ldn", (long)i);

In addition to the considerations mentioned in Table 2, there is one extra case with scanning: you must distinguish the types for float and double. You should use %f for float,%lf for double. If you need to use scanf (or a variant thereof) with CGFloat, switch to double instead, and copy the double to CGFloat.

CGFloat imageWidth;
double tmp;
sscanf (str, "%lf", &tmp);
imageWidth = tmp;

It is important to remember that %lf does not represent CGFloat correctly on either 32- or 64-bit platforms. This is unlike %ld, which works for long in all cases.

ที่มา: http://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/Strings/Articles/formatSpecifiers.html