iOS版/ C：转换＆QUOT;整数QUOT;到四个字符的字符串 [英] iOS/C: Convert "integer" into four character string

问题描述

很多与音频会话编程相关的常量是真正的四字符串（<一个href=\"http://developer.apple.com/library/ios/documentation/AudioToolbox/Reference/AudioSessionServicesReference/Reference/reference.html#//apple_ref/doc/uid/TP40007915-CH6-SW2\"相对=nofollow>音频会话服务参考）。这同样适用于在<一个href=\"http://developer.apple.com/library/ios/documentation/AudioToolbox/Reference/AudioSessionServicesReference/Reference/reference.html#//apple_ref/doc/uid/TP40007915-CH7a-SW1\"相对=nofollow> OSStatus code 从函数返回象 AudioSessionGetProperty 。

A lot of the constants associated with Audio Session programming are really four-character strings (Audio Session Services Reference). The same applies to the OSStatus code returned from functions like AudioSessionGetProperty.

问题是，当我尝试打印这些东西开箱，它们看起来像1919902568.我可以把它插入到计算机并打开ASCII输出，它会告诉我蓉城，但必须有一个编程的方式来做到这一点。

The problem is that when I try to print these things out of the box, they look like 1919902568. I can plug that into Calculator and turn on ASCII output and it'll tell me "roch", but there must be a programmatic way to do this.

我已经有限的成功具有以下块我的C功能之一：

I've had limited success in one of my C functions with the following block:

char str[20];
// see if it appears to be a four-character code
*(UInt32 *) (str + 1) = CFSwapInt32HostToBig(error);
if (isprint(str[1]) && isprint(str[2]) && isprint(str[3]) && isprint(str[4])) {
    str[0] = str[5] = '\'';
    str[6] = '\0';
} else {
    // no, format as integer
    sprintf(str, "%d", (int)error);
}

我想要做的是抽象的这个功能摆脱目前的功能，以便在其他地方使用它。我试图做

What I want to do is to abstract this feature out of its current function, in order to use it elsewhere. I tried doing

char * fourCharCode(UInt32 code) {
    // block
}
void someOtherFunction(UInt32 foo){
    printf("%s\n",fourCharCode(foo));
}

但给了我A *€/3íT：E *€/ +€/，而不是蓉城。我的C福不是很强，但我的直觉是，上述code试图间preT的内存地址为一个字符串。或者，也许有一个编码问题？任何想法？

but that gives me "à*€/3íT:ê*€/+€/", not "roch". My C fu isn't very strong, but my hunch is that the above code tries to interpret the memory address as a string. Or perhaps there's an encoding issue? Any ideas?

推荐答案

你在谈论的类型是 FourChar code 在<$ C定义$ C> CFBase.h 。它相当于一个 OSTYPE 。最简单的方式之间的转换 OSTYPE 和的NSString 使用 NSFileTypeForHFSType code（） 和 NSHFSType codeFromFileType（）。这些功能，遗憾的是，不可用在iOS上。

The type you're talking about is a FourCharCode, defined in CFBase.h. It's equivalent to an OSType. The easiest way to convert between OSType and NSString is using NSFileTypeForHFSTypeCode() and NSHFSTypeCodeFromFileType(). These functions, unfortunately, aren't available on iOS.

有关iOS和可可便携code，我喜欢约阿希姆·本特松的 FourCC2Str（）从他 NCCommon.h （加为方便使用一个小铸造清理）：

For iOS and Cocoa-portable code, I like Joachim Bengtsson's FourCC2Str() from his NCCommon.h (plus a little casting cleanup for easier use):

#include <TargetConditionals.h>
#if TARGET_RT_BIG_ENDIAN
#   define FourCC2Str(fourcc) (const char[]){*((char*)&fourcc), *(((char*)&fourcc)+1), *(((char*)&fourcc)+2), *(((char*)&fourcc)+3),0}
#else
#   define FourCC2Str(fourcc) (const char[]){*(((char*)&fourcc)+3), *(((char*)&fourcc)+2), *(((char*)&fourcc)+1), *(((char*)&fourcc)+0),0}
#endif

FourCharCode code = 'APPL';
NSLog(@"%s", FourCC2Str(code));
NSLog(@"%@", @(FourCC2Str(code));

您当然可以扔 @（）进入宏更容易使用。

You could of course throw the @() into the macro for even easier use.

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