IOS String Format Specifiers
| 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 a, A, e, E, f, F, g, 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 d, i, o, u, x, or X conversion specifier applies to a size_t or the corresponding signed integer type argument |
%t |
Length modifier specifying that a following d, i, o, u, x, or X conversion specifier applies to a ptrdiff_t or the corresponding unsigned integer type argument |
%j |
Length modifier specifying that a following d, i, o, u, x, or X conversion specifier applies to a intmax_t or uintmax_t argument |
Platform Dependencies
Mac OS X uses several data types—NSInteger, NSUInteger,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.
| 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.
