【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

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

NSData 转换成NSString对象

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

NSData 转换成char*

NSData *data;

2 char *test=[data bytes];

char* 转换成NSData对象

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

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

 

 1. NSString转化为UNICODE String：

  (NSString*)fname ＝ @“Test”; 
 char fnameStr[];
  memcpy(fnameStr, [fname cStringUsingEncoding:NSUnicodeStringEncoding], *([fname length])); 

与strcpy相比，memcpy并不是遇到'\0'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：
1 char * a = (char*)malloc(sizeof(byte)*); 

 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:] stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding ]];
 NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
 [request setHTTPMethod:@"POST"]; 

 NSMutableArray *_array = [[NSMutableArray alloc] initWithCapacity:];
 for (int i = ; 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];