If I have
NSString *myString = #"string for data1"
const char *utfMyString = [myString UTF8String];
NSLog(#"length of my myString is %d",[myString length]);
NSLog(#"length of my utfMyString is %lu",strlen(utfMyString));
I looked up the definition of method UTF8String which returns a null terminated at the end for the receiver. Therefore, i think length of utfMyString should be 17.
Unfortunately, utfMyString still is length of 16.
Please correct me about this issue. Thanks a lot
strlen() doesn't include the terminating null character in its length count.
Related
I am doing a socket connection and writing a data through a socket,I need to and null string at end of my data like,
myMethod=ABC||10D=12345||phNumber=zzz||lang=english and at last after english I need to append null string,please help me with this.
Simply append NULL word which is : "\0"
NSString *nullEndedString = #"myMethod=ABC||10D=12345||phNumber=zzz||lang=english\0";
\0 means NULL
You can add null at the beginning of the character by using
char bytes[] = "\0name\0surname";
NSString * mystring = [NSString mystring];
[mystring initWithBytes:bytes length:sizeof(bytes)];
NSData * data = [mystring dataUsingEncoding:NSUTF8StringEncoding];
You can use above code according to your functionality.
hey just a couple quick noob questions about writing my first ios app. Ive been searching through the questions here but they all seem to address questions more advanced than mine so im getting confused.
(1) All I want to do is turn a string into an array of integers representing the ASCII code. In other words, I want to convert:
"This is some string. It has spaces, punctuation, AND capitals."
into an array with 62 integers.
(2) How do I get back from the NSArray to a string?
(3) Also, are these expensive operations in terms of memory or computation time? It seems like it might be if we have to create a new variable at every iteration or something.
I know how to declare all the variables and im assuming I run a loop through the length of the string and at each iteration I somehow get the character and convert it into a number with some call to a built in command.
Thanks for any help you can offer or links to posts that might help!
if you want to store the ascii values in an nsarray it is going to be expensive. NSArray can only hold objects so you're going to have to create an NSNumber for each ASCII value:
unsigned len = [string length];
NSMutableArray arr = [NSMutableArray arrayWithCapacity:len];
for (unsigned i = 0; i < len; ++i) {
[arr addObject:[NSNumber numberWithUnsignedShort:[string characterAtIndex:i]]];
}
2) to go back to an NSString you'll need to use an MSMutableString and append each byte to the NSMutableString.
After saying that I'd suggest you don't use this method if you can avoid it.
A better approach would be to use #EmilioPelaez's answer. To go back from a memory buffer to an NSString is simple and inexpensive compared to iterating and concatting strings.
NSString * stringFromMemory = [[NSString alloc] initWithBytes:buffer length:len encoding: NSASCIIStringEncoding];
I ended up using the syntax I found here. Thanks for the help
How to convert ASCII value to a character in Objective-C?
NSString has a method to get the characters in an array:
NSString *string = "This is some string. It has spaces, punctuation, AND capitals.";
unichar *buffer = malloc(sizeof(unichar) * [string lenght]);
[string getCharacters:buffer range:NSMakeRange(0, [string length])];
If you check the definition of unichar, it's an unsigned short.
This code SHOULD clean phone number, but it doesn't:
NSLog(#"%#", self.textView.text);
// Output +358 40 111 1111
NSString *s = [self.textView.text stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
NSLog(#"%#", s);
// Output +358 40 111 1111
Any ideas what is wrong? Any other ways to remove whitespacish characters from text string (except the hard way)?
Try this
NSCharacterSet *dontWantChar = [NSCharacterSet whitespaceAndNewlineCharacterSet];
NSString *string = [[self.textView.text componentsSeparatedByCharactersInSet:dontWantChar] componentsJoinedByString:#""];
The documentation for stringByTrimmingCharactersInSet says:
Returns a new string made by removing from both ends of the
receiver characters contained in a given character set.
In other words, it only removes the offending characters from before and after the string any valid characters. Any "offending" characters are left in the middle of the string because the trim method doesn't touch that part.
Anyways, there are a few ways to do the thing you're trying to do (and #Narayana's answer is good on this, too... +1 to him/her). My solution would be to set your string s to be a mutable string and then do:
[s replaceOccurrencesOfString: #" " withString: #"" options: NSBackwardsSearch range: NSMakeRange( 0, [s length] )];
I wanna encpryt a string with a key, using HmacSHA256. The code everyone use is the one below, but there is one thing that doesn´t make sense.
Why would we use base64 at the end if all we want is the HmacSHA256 hash?
I tried seeing the hash generated after the method CCHmac is called with
NSString *str = [[NSString alloc] initWithData:HMAC encoding:NSASCIIStringEncoding];
NSLog(#"%#", str);
But i don´t get the hash generated, i get null, or garbage, like this:
2011-10-11 09:38:05.082 Hash_HmacSHA256[368:207] (null)
2011-10-11 09:38:05.085 Hash_HmacSHA256[368:207] Rwªb7iså{yyþ§Ù(&oá÷ÛËÚ¥M`f
import < CommonCrypto/CommonHMAC.h>
NSString *key;
NSString *data;
const char *cKey = [key cStringUsingEncoding:NSASCIIStringEncoding];
const char *cData = [data cStringUsingEncoding:NSASCIIStringEncoding];
unsigned char cHMAC[CC_SHA256_DIGEST_LENGTH];
CCHmac(kCCHmacAlgSHA256, cKey, strlen(cKey), cData, strlen(cData), cHMAC);
NSData *HMAC = [[NSData alloc] initWithBytes:cHMAC
length:sizeof(cHMAC)];
NSString *hash = [HMAC base64Encoding]; //This line doesn´t make sense
[key release];
[data release];
First of all, for those wondering, this is in reference to my answer to this question: Objective-C sample code for HMAC-SHA1
The HMAC you generate is a 256-bit binary value that may or may not start with a 0 byte.
To be able to print it, you need a string representation (binary, hex, decimal, base64, etc.). Base64 is one of the most efficient among these, that's why I used a Base64 encoding there.
The reason you get garbage is that most (if not all) of the octets in the HMAC value are outside the range of printable ASCII characters. If the first octet is 0 (0x00), you get nil. This is why you need an encoding that supports arbitrary values. ASCII doesn't.
Of course, if you don't want to print the HMAC value, then may not need such an encoding, and can keep the HMAC as is (binary NSData).
I spend a whole day, trying to convert the generated hash (bytes) into readable data. I used the base64 encoded you said and it didn´t work at all for me .
So what i did was this:
CCHmac(kCCHmacAlgSHA256, cKey, strlen(cKey), cData, strlen(cData), cHMAC);
// Now convert to NSData structure to make it usable again
NSData *out = [NSData dataWithBytes:cHMAC length:CC_SHA256_DIGEST_LENGTH];
// description converts to hex but puts <> around it and spaces every 4 bytes
NSString *hash = [out description];
hash = [hash stringByReplacingOccurrencesOfString:#" " withString:#""];
hash = [hash stringByReplacingOccurrencesOfString:#"<" withString:#""];
hash = [hash stringByReplacingOccurrencesOfString:#">" withString:#""];
// hash is now a string with just the 40char hash value in it
NSLog(#"%#",hash);
Don't do "[out description]" to get the hash as a string.
Do [hash base64Encoding] to get the base64 encoding of it. Use http://cybersam.com/ios-dev/http-basic-access-authentication-with-objective-c-and-ios/attachment/nsdataadditions to get the base64Encoding function. The additions class is a category that will add the function base64Encoding to NSData's implementation.
Or you can do [[NSString alloc]initWithData:out encoding:NSUTF8StringEncoding].
when i use this code for generate an hash256 in my iPhone app:
unsigned char hashedChars[32];
NSString *inputString;
inputString = [NSString stringWithFormat:#"hello"];
CC_SHA256([inputString UTF8String],
[inputString lengthOfBytesUsingEncoding:NSASCIIStringEncoding ],
hashedChars);
NSData * hashedData = [NSData dataWithBytes:hashedChars length:32];
The hash256 of inputString, is created correctly, but if i use a string like this #"\x00\x25\x53\b4", the hash256 is different from the real string with "\x" characters.
I think that the problem is in encoding "UTF8" instead of ascii.
Thanks!
I would be suspicious of the first character, "\x00" - thats going to terminate anything that thinks its dealing with "regular C strings".
Not sure whether lengthOfBytesUsingEncoding: takes that stuff into account, but its something I'd experiment with.
You're getting the bytes with [inputString UTF8String] but the length with [inputString lengthOfBytesUsingEncoding:NSASCIIStringEncoding]. This is obviously wrong. Moreover (assuming you mean "\xB4" and that it turns into something not in ASCII), "\xB4" is not likely to be in ASCII. The docs for NSString say
Returns 0 if the specified encoding cannot be used to convert the receiver
So you're calculating the hash of the empty string. Of course it's wrong.
You're less likely to have problems if you only generate the data once:
NSData * inputData = [inputString dataUsingEncoding:NSUTF8StringEncoding];
CC_SHA256(inputData.bytes, inputData.length, hashedChars);