Object-C 中各数据类型转换 NSData转NSString，Byte，UIImage

1. NSString转化为UNICODE String：
(NSString*)fname ＝ @“Test”;
char fnameStr[10];
memcpy(fnameStr, [fname cStringUsingEncoding:NSUnicodeStringEncoding], 2*([fname length]));

与strcpy相比，memcpy并不是遇到''就结束，而是一定会拷贝完n个字节

2. NSString 转化为 char *
NSString * str＝ @“Test”;
const char * a =[str UTF8String];

3.char * 转化为 NSString

NSString *str=[NSString stringWithCString  encoding:NSUTF8StringEncoding];

4. char * 转化 NSData
 方法一：
   char * a = (char*)malloc(sizeof(byte)*16);
   NSData *data = [NSData dataWithBytes: a   length:strlen(a)];
 方法二：
    转换为NSString： - (id)initWithUTF8String:(const char *)bytes
    然后用NSString的 - (NSData *)dataUsingEncoding:(NSStringEncoding)encoding

5. NSData 转化 char *
  NSData data ；
  char* a=[data bytes];

6. NSData 转化 NSString;

NSData* data;

NSString* aStr= ［NSString alloc] initWithData:data   encoding:NSASCIIStringEncoding];

7. NSString 转化 NSData对象
NSData* xmlData = [@"testdata" dataUsingEncoding:NSUTF8StringEncoding];

NSString 转化 NSURL  

 //NSURL *url = [NSURL URLWithString:[str   stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding ]]; 

NSString *urlString=[@"http://www.google.com/search?client=safari&rls=en&q=搜索&ie=UTF-8&oe=UTF-8" stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

NSURL 转化 NSString

NSURL *url=[NSURL URLWithString:urlString];

NSString *s=[[url absoluteString] stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

NSArray *arr = [urlStr componentsSeparatedByString:@"&"]; 
NSURL *url = [NSURL URLWithString:[[arr objectAtIndex:0] stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding ]]; 
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url]; 
[request setHTTPMethod:@"POST"]; 



NSMutableArray *_array = [[NSMutableArray alloc] initWithCapacity:0]; 
for (int i = 1; i < [arr count]; ++i ){ 
NSString *str = [arr objectAtIndex:i]; 
[_array addObject:str]; 
} 
[_array componentsJoinedByString:@"&"]; 
NSData *data = [[_array componentsJoinedByString:@"&"] dataUsingEncoding: NSASCIIStringEncoding]; 
[request setHTTPBody:data];

 // 发送请求并获得服务器反馈的数据
    NSData *urldata = [AESEnCDeCViewController Get:url];
    // 第一种 转换NSData数据到char*字符串
    char * test = (char*)[urldata bytes];
    std::string old = deaes(test);



    // 第二种 转换NSData到UTF8编码的NSString中再转换为char*字符串

//    NSString *desStr = [[NSString alloc] initWithData:urldata encoding:NSUTF8StringEncoding];

//    const char *desresult = [desStr UTF8String];

//    std::string old = deaes(desresult);

    

    // 解密字字符串到明文

    NSString *oldstr = [[NSString alloc] initWithCString:old.c_str()];

很多时候软件读取的中文网页编码集是gb2312，所以显示出来的是乱码。这时需要将NSString文字编码转换

1 NSURL *url = [NSURL URLWithString:urlStr];

2 NSData *data = [NSData dataWithContentsOfURL:url];    

3 NSStringEncoding enc = CFStringConvertEncodingToNSStringEncoding(kCFStringEncodingGB_18030_2000);    

4 NSString *retStr = [[NSString alloc] initWithData:data encoding:enc];

详细代码

1，NSData 与 NSString
　　NSData --> NSString
　　NSString *aString = [[NSString alloc] initWithData:adata encoding:NSUTF8StringEncoding];
　　NSString --> NSData
　　NSString *aString = @"1234";
　　NSData *aData = [aString dataUsingEncoding: NSUTF8StringEncoding];

2，NSData 与 Byte
　　NSData --> Byte
　　NSString *testString = @"1234567890";
　　NSData *testData = [testString dataUsingEncoding: NSUTF8StringEncoding];
　　Byte *testByte = (Byte *)[testData bytes];
　　Byte --> NSData
　　Byte byte[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23};
　　NSData *adata = [[NSData alloc] initWithBytes:byte length:24];

3，NSData 与 UIImage
　　NSData --> UIImage
　　UIImage *aimage = [UIImage imageWithData: imageData];
　　//例：从本地文件沙盒中取图片并转换为NSData
　　NSString *path = [[NSBundle mainBundle] bundlePath];
　　NSString *name = [NSString stringWithFormat:@"ceshi.png"];
　　NSString *finalPath = [path stringByAppendingPathComponent:name];
　　NSData *imageData = [NSData dataWithContentsOfFile: finalPath];
　　UIImage *aimage = [UIImage imageWithData: imageData];
　　UIImage－> NSData
　　NSData *imageData = UIImagePNGRepresentation(aimae);

4，NSData 与 NSMutableData
　　NSData --> MSMutableData
　　NSData *data=[[NSData alloc]init];
　　NSMutableData *mdata=[[NSMutableData alloc]init];   
　　mdata=[NSData dataWithData:data];

5，NSData合并为一个NSMutableData

- (NSString *)filePathWithName:(NSString *)filename
 {
         NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
         NSString *documentsDirectory = [paths objectAtIndex:0];
         return [documentsDirectory stringByAppendingPathComponent:filename];
 }
 
 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    
     //音频文件路径
         NSString *mp3Path1 = [[NSBundle mainBundle] pathForResource:@"1" ofType:@"mp3"];
         NSString *mp3Path2 = [[NSBundle mainBundle] pathForResource:@"2" ofType:@"mp3"];
         //音频数据
         NSData *sound1Data = [[NSData alloc] initWithContentsOfFile: mp3Path1];
         NSData *sound2Data = [[NSData alloc] initWithContentsOfFile: mp3Path2];
         //合并音频
         NSMutableData *sounds = [NSMutableData alloc];
         [sounds appendData:sound1Data];
         [sounds appendData:sound2Data];
         //保存音频
 
         NSLog(@"data length:%d", [sounds length]);
 
         [sounds writeToFile:[self filePathWithName:@"tmp.mp3"] atomically:YES];
         
         [window makeKeyAndVisible];
     
     return YES;
 }