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)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:NSUTF8StringEncoding];

7. NSString 转化 NSData对象

NSData* xmlData = [@"testdata" dataUsingEncoding:NSUTF8StringEncoding];
8.NSString输出CGPoint
    UIButton *buttn=[UIButtonbuttonWithType:UIButtonTypeRoundedRect];
    buttn.frame=CGRectMake(0, 2, 100, 100);
    NSLog(@"===%@",NSStringFromCGRect(buttn.frame));   //输出CGpoint和CGrect
9.中文与utf8相互转换
    NSString *str=@"老大-老二";
    NSString *ss=[str stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]; //向网络传中文字符串要转换为utf8字符串再传,utf8码也是放在nsstring里的
    NSString *str2=[ss stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];   //utf8转换成中文字符串
    NSLog(@"%@++\n",str);
    NSLog(@"%@--\n",ss);
    NSLog(@"%@==\n",str2);
10.NSString转换成NSArray
    NSArray *array=[str componentsSeparatedByString:@"-"];
    for (int i=0; i<2; i++) {
        NSLog(@"++%@++\n",[array objectAtIndex:i]);
    }

11.NSString 转化 NSURL  

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

NSURL *url = [NSURL URLWithString:urlString]; 

12.NSURL 转化 NSString

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

NSArray *arr = [urlString 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];