转自网络：

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'\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：   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)encoding5. 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()];