oc 前缀格式

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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 longNSUInteger%lu or %lxCast the value to unsigned longCGFloat%f or %g%f works for floats and doubles when formatting; but see below warning when scanningCFIndex%ld or %lxThe same as NSIntegerpointer%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 platformsunsigned 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.

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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.

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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.

基本数据类型

1. int
输出格式符：%i, %d, %o %x,

2. float
输出格式符：%f, %e, %g

3. double
输出格式符：%f, %e, %g

4. char

输出格式符：%c

限定符：

1. long
long int: %li
long double: %Lf
形成long int通过在数字后面加L.
long int number = 123324123234123L;

2. long long
long long int: %lli

3. short
short int: %hi

4. unsigned

5. signed

它们各自所占的字节数

#import<Foundation/Foundation.h>

int main (int argc,const char * argv[]) {

NSAutoreleasePool * pool = [[NSAutoreleasePoolalloc] init];

NSLog(@"The size of an int is: %d bytes.",sizeof(int));

NSLog(@"The size of a short int is: %d bytes.",sizeof(shortint));

NSLog(@"The size of a long int is: %d bytes.",sizeof(longint));

NSLog(@"The size of a char is: %d bytes.",sizeof(char));

NSLog(@"The size of a float is: %d bytes.",sizeof(float));

NSLog(@"The size of a double is: %d bytes.",sizeof(double));

NSLog(@"The size of a bool is: %d bytes.",sizeof(bool));

[pool drain];

return 0;

}

2011-08-21 09:29:16.475 sizeofTest[860:903] The size of an int is: 4 bytes.

2011-08-21 09:29:16.478 sizeofTest[860:903] The size of a short int is: 2 bytes.

2011-08-21 09:29:16.478 sizeofTest[860:903] The size of a long int is: 8 bytes.

2011-08-21 09:29:16.479 sizeofTest[860:903] The size of a char is: 1 bytes.

2011-08-21 09:29:16.479 sizeofTest[860:903] The size of a float is: 4 bytes.

2011-08-21 09:29:16.479 sizeofTest[860:903] The size of a double is: 8 bytes.

2011-08-21 09:29:16.480 sizeofTest[860:903] The size of a bool is: 1 bytes.

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