iOS NSString / NSData / char* 类型之间的转换

一、感谢大神分享（如果看不了原文章，请科学上网）：http://www.cnblogs.com/pengyingh/articles/2341880.html

二、
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

1. 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];

1. 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

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

3. NSData 转化 NSString;
   NSData* data;
   NSString* aStr= ［NSString alloc] initWithData:data encoding:NSASCIIStringEncoding];

4. NSString 转化 NSData对象

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

http://blog.sina.com.cn/s/articlelist_1256141290_14_1.html

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];