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Objective-C NSString formatting

The format specifiers supported by the NSString formatting methods and CFString formatting
functions follow the IEEE printf specification; the specifiers are summarized in Table 1.
Note that you can also use the “n$” positional specifiers such as %1$@ %2$s.
For more details, see the IEEE printf specification. You can also use these format specifiers with the NSLog function.

Table 1 Format specifiers supported by the NSString formatting methods and CFString formatting functions
定义说明
%@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, %iSigned 32-bit integer (int)
%u, %UUnsigned 32-bit integer (unsigned int)
%hiSigned 16-bit integer (short)
%huUnsigned 16-bit integer (unsigned short)
%qiSigned 64-bit integer (long long)
%quUnsigned 64-bit integer (unsigned long long)
%xUnsigned 32-bit integer (unsigned int), printed in hexadecimal using the digits 0–9 and lowercase a–f
%XUnsigned 32-bit integer (unsigned int), printed in hexadecimal using the digits 0–9 and uppercase A–F
%qxUnsigned 64-bit integer (unsigned long long), printed in hexadecimal using the digits 0–9 and lowercase a–f
%qXUnsigned 64-bit integer (unsigned long long), printed in hexadecimal using the digits 0–9 and uppercase A–F
%o, %OUnsigned 32-bit integer (unsigned int), printed in octal
%f64-bit floating-point number (double)
%e64-bit floating-point number (double), printed in scientific notation using a lowercase e to introduce the exponent
%E64-bit floating-point number (double), printed in scientific notation using an uppercase E to introduce the exponent
%g64-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
%G64-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
%c8-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
%C16-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
%sNull-terminated array of 8-bit unsigned characters. %s interprets its input in the system encoding rather than, for example, UTF-8.
%SNull-terminated array of 16-bit Unicode characters
%pVoid pointer (void *), printed in hexadecimal with the digits 0–9 and lowercase a–f, with a leading 0x
%LLength modifier specifying that a following a, A, e, E, f, F, g, or G conversion specifier applies to a long double argument
%a64-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
%A64-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
%F64-bit floating-point number (double), printed in decimal notation
%zLength 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
%tLength 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
%jLength modifier specifying that a following d, i, o, u, x, or X conversion specifier applies to a intmax_t or uintmax_t argument


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 long and 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
类型定义建议
NSInteger%ld or %lxCast the value to long
NSUInteger%lu or %lxCast 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 %lxThe 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 %llxlong long is 64-bit on both 32- and 64-bit platforms
unsigned long long%llu or %llxunsigned 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.

1
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NSInteger i = 42;
printf("%ld\n", (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.

1
2
3
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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.





posted on 2012-03-04 00:27 gembin 阅读(806) 评论(0)  编辑  收藏 所属分类: Objective-C


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