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.

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, %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 |

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.

类型 | 定义 | 建议 |

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.

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