NSString -> string
String str =[aNSString UTF8String]; //aNSString是NSString的值
String -> NSString
NSString * nss = [NSString stringWithUTF8String:str.c_str()];
NSString -> string
String str =[aNSString UTF8String]; //aNSString是NSString的值
String -> NSString
NSString * nss = [NSString stringWithUTF8String:str.c_str()];