常用的一些占位符：

%@：字符串占位符

%d:整型

%ld:長整型

%f:浮點型

%c:char類型

%%：%的占位符

盡管有那么多的占位符，但是好像沒有發現BOOL型的數據的占位符，這也是比較糾結的地方，看了一下別人是怎么解決這個問題的

[cpp]?view plaincopyprint?

BOOL?studyBool?=?YES;??

???????NSLog(@"打印BOOL型數據%@",studyBool?@"YES":@"NO");//打印BOOL型數據YES??

???????NSLog(@"打印BOOL型數據%d",studyBool);//打印BOOL型數據1??

?????????

???????BOOL?alsoBool?=?NO;??

???????NSLog(@"打印BOOL型數據%@",alsoBool?@"YES":@"NO");//打印BOOL型數據NO??

???????NSLog(@"打印BOOL型數據%d",alsoBool);//打印BOOL型數據0??

詳細介紹：**********************************************************

%@: ? ? ? ? ? ? Objective-C對象,印有字符串返回descriptionWithLocale:如果于的話,或描述相反.CFTypeRef工作對象,返回的結果的CFCopyDescription功能.(這個翻譯有問題建議按照自己的理解方式理解)。

%%: ? ? ? ? ? ? 為'%'字符;

%d,%D,%i: ? 為32位整型數(int);

%u,%U: ? ? ? ?為32位無符號整型數(unsigned int);

%hi: ? 為有符號的16位整型數(short);

%hu: ?為無符號的16位整型數(unsigned shord);

%qi: ? 為有符號的64位整型數(long long);

%qu: ?為無符號的64位整型數(unsigned long long);

%x: ? ?為32位的無符號整型數(unsigned int),打印使用數字0-9的十六進制,小寫a-f;

%X: ? ?為32位的無符號整型數(unsigned int),打印使用數字0-9的十六進制,大寫A-F;

%qx: ? 為無符號64位整數(unsigned long long),打印使用數字0-9的十六進制,小寫a-f;

%qX: ? 為無符號64位整數(unsigned long long),打印使用數字0-9的十六進制,大寫A-F;

%o,%O: ? 為32位的無符號整數（unsigned int),打印八進制數;

%f: ? ? ?為64位的浮點數(double);

%e: ? ? ?為64位的浮點數(double),打印使用小寫字母e,科學計數法介紹了指數的增大而減小;

%E: ? ? ?為64位的浮點數(double),打印科學符號使用一個大寫E介紹指數的增大而減小;

%g: ? ? ?為64位的浮點數(double),用%e的方式打印指數,如果指數小于4或者大于等于精度,那么%f的風格就會有不同體現;

%G: ? ? ?為64位的浮點數(double),用%E的方式打印指數,如果指數小于4或者大于等于精度,那么%f的風格就會有不同體現;

%c: ? ? ? 為8位的無符號字符%c(unsigned char),通過打印NSLog()將其作為一個ASCII字符,或者,不是一個ASCII字符,八進制格式\ddd或統一標準的字符編碼的十六進制格式\udddd,在這里d是一個數字;

%C: ? ? ? 為16位Unicode字符%C(unichar),通過打印NSLog()將其作為一個ASCII字符,或者,不是一個ASCII字符,八進制格式\ddd或統一標準的字符編碼的十六進制格式\\udddd,在這里d是一個數字;

%s: ? ? ? 對于無符號字符數組空終止,%s系統中解釋其輸入編碼,而不是別的,如utf-8;

%S: ? ? ? 空終止一系列的16位Unicode字符;

%p: ? ? ? 空指針(無效*)，打印十六進制的數字0-9和小寫a-f,前綴為0x;

%L: ? ? ? 在明確規定的長度下,進行修正,下面的一批數據a,A,e,E,f,F,g,G應用于雙精度長整型的參數;

%a: ? ? ? 為64位的浮點數(double),按照科學計數法打印采用0x和一個十六進制數字前使用小寫小數點p來介紹指數的增大而減小;

%A: ? ? ? 為64位的浮點數(double),按照科學計數法打印采用0X和一個十六進制數字前使用大寫字母小數點P界掃指數的增大而減小；

%F: ? ? ? 為64位的浮點數(double),按照十進制表示法進行打印；

%z: ? ? ? 修改說明在%z長度以下d,i,o,u,x,X適用于某一指定類型的轉換或者適用于一定尺寸的整數類型的參數;

%t: ? ? ? 修改說明在%t長度以下d,i,o,u,x,X適用于某一指定類型或一定尺寸的整數類型的轉換的參數;

%j: ? ? ? 修改說明在%j長度以下d,i,o,u,x,X適用于某一指定類型或一定尺寸的整數類型的轉換的參數。

英文文檔

格式定義
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

定義	說明
%@	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, %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

平臺依賴
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

類型	定義	建議
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.

1 2	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 4

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.

總結

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