【转】NSString / NSData / char* 类型之间的转换

原文：http://www.cnblogs.com/pengyingh/articles/2341880.html

NSString 转换成NSData 对象

1 NSData* xmlData = [@"testdata" dataUsingEncoding:NSUTF8StringEncoding];

NSData 转换成NSString对象

1 NSData * data; 2 NSString *result = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

NSData 转换成char*

1 NSData *data;

2 char *test=[data bytes];

char* 转换成NSData对象

1 byte* tempData = malloc(sizeof(byte)*16);

2 NSData *content = [NSData dataWithBytes:tempData length:16];

1. NSString转化为UNICODE String：


 1 (NSString*)fname ＝ @“Test”; 
 2 char fnameStr[10];
 3 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 *

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

3.char * 转化为 NSString

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

4. char * 转化 NSData
 方法一：

1 char * a = (char*)malloc(sizeof(byte)*16); 

2 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 *

 1  NSData data ；

 2 char* a=[data bytes]; 


6. NSData 转化 NSString;

 1 NSData* data;

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

7. NSString 转化 NSData对象

 1 NSData* xmlData = [@"testdata" dataUsingEncoding:NSUTF8StringEncoding];

NSString 转化 NSURL

1  //NSURL *url = [NSURL URLWithString:[str   stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding ]]; 
2 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

 1 NSURL *url=[NSURL URLWithString:urlString];
 2 NSString *s=[[url absoluteString] stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
 3 NSArray *arr = [urlStr componentsSeparatedByString:@"&"]; 
 4 NSURL *url = [NSURL URLWithString:[[arr objectAtIndex:0] stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding ]]; 
 5 NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url]; 
 6 [request setHTTPMethod:@"POST"]; 
 7 
 8 NSMutableArray *_array = [[NSMutableArray alloc] initWithCapacity:0]; 
 9 for (int i = 1; i < [arr count]; ++i ){ 
10 NSString *str = [arr objectAtIndex:i]; 
11 [_array addObject:str]; 
12 } 
13 [_array componentsJoinedByString:@"&"]; 
14 NSData *data = [[_array componentsJoinedByString:@"&"] dataUsingEncoding: NSASCIIStringEncoding]; 
15 [request setHTTPBody:data];
16  // 发送请求并获得服务器反馈的数据
17     NSData *urldata = [AESEnCDeCViewController Get:url];
18     
19     // 第一种 转换NSData数据到char*字符串
20     char * test = (char*)[urldata bytes];
21     std::string old = deaes(test);
22     
23     // 第二种 转换NSData到UTF8编码的NSString中再转换为char*字符串
24 //    NSString *desStr = [[NSString alloc] initWithData:urldata encoding:NSUTF8StringEncoding];
25 //    const char *desresult = [desStr UTF8String];
26 //    std::string old = deaes(desresult);
27     
28     // 解密字字符串到明文
29     NSString *oldstr = [[NSString alloc] initWithCString:old.c_str()];
30

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];