Converting NSString to char byte array

Question

In my program, I receive a NSString like this one : AA010158AA7D385002. And I need to pass it to a method which accept a char byte array, as below :

char[9] = {0xAA, 0x01, 0x01, 0x58, 0xAA, 0x7D, 0x38, 0x50, 0x02};

How to convert my NSString to char byte array like this one?

Thanks!

check this http://stackoverflow.com/questions/11087031/how-to-convert-an-initwithbytes-nsstring-to-unsigned-char?rq=1 — Jigar, Mar 29 '17 at 08:02
@MianShahbazAkram in my example String, I would like "AA" to give the result "0xAA" as a byte that I can pass in my char array. — fraxool, Mar 29 '17 at 08:15
@fraxool bro i have updated answer check if its working for you.. — Mukesh Lokare, Mar 29 '17 at 08:22
@Mukesh I saw your answer which gave an "out of bounds" error... — fraxool, Mar 29 '17 at 09:06
Ah, you have a hexadecimal string and want to convert each pair of hex digits into the corresponding char? What Encoding are these bytes in? — uliwitness, Mar 29 '17 at 15:43

score 1 · Answer 1 · answered Mar 29 '17 at 08:06

1

 NSString *strCharData = @"AA010158AA7D385002";
 const char *characterRes = [strCharData cStringUsingEncoding:NSUTF8StringEncoding]; 

      or

 NSString *strCharData = @"AA010158AA7D385002";
 const char *characterRes = [strCharData UTF8String];

answered Mar 29 '17 at 08:06

user3182143

9,459
3
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Mukesh Lokare · Answer 2 · 2017-03-29T09:31:23.070

0

Use this answer if i am correct,i did little coding but might be there are possibilities of simpler solutions also like @user3182143

NSString * inputStr = @"AA010158AA7D385002";
NSMutableArray *charByteArray = [[NSMutableArray alloc]initWithCapacity:1];
int i = 0;
for (i = 0; i+2 <= inputStr.length; i+=2) {

    NSRange range = NSMakeRange(i, 2);
    NSString* charStr = [inputStr substringWithRange:range];
    [charByteArray addObject:[NSString stringWithFormat:@"0x%@",charStr]];

}

Output :

char[9] = ( 0xAA, 0x01, 0x01, 0x58, 0xAA, 0x7D, 0x38, 0x50, 0x02 )

edited Mar 29 '17 at 09:31

answered Mar 29 '17 at 08:14

Mukesh Lokare

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26
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That wouldn't give a char[9] like the OP asked, that would give an NSArray. – uliwitness Mar 29 '17 at 09:00
@uliwitness What it mean NSArray can you explain me please ? You know we can convert it into NSArray by copy & it will also gives same output. :D – Mukesh Lokare Mar 29 '17 at 09:19
@Mukesh if you can update your answer with the output as a char[9], I will accept your answer. – fraxool Mar 29 '17 at 09:22
@fraxool welcome :) but we have 9 array object that mean 0..8 index, good luck – Mukesh Lokare Mar 29 '17 at 09:30
@fraxool accept & up my answer if it helps for you. – Mukesh Lokare Mar 29 '17 at 09:50
@Mukesh I have upped it, but I can't accept until I get a char array as the result. – fraxool Mar 29 '17 at 09:51

uliwitness · Answer 3 · 2017-03-29T16:02:16.060

Since your text is hex and you want actual bytes out (which each correspond to two hex characters), you'll have to manually convert each character into the corresponding number, and then add them together into the correct numerical value.

To do this, I'm taking advantage of the fact that, in ASCII characters, a...z are in a row, as are 0...9. I'm also taking advantage of the fact that hexadecimal is valid ASCII, and that Unicode characters from 0...127 are identical to their corresponding ASCII characters.

Below is a program that does this and prints out the original string's characters as well as the calculated bytes (as hex again):

#import <Foundation/Foundation.h>

int main(int argc, char *argv[])
{
    @autoreleasepool
    {
        NSString *hexStr = @"1234567890abcdef12";
        unsigned char theBytes[9] = {};
        for( NSUInteger x = 0; x < sizeof(theBytes); x++ )
        {
            unsigned char digitOne = [hexStr characterAtIndex: x * 2];
            if( digitOne >= 'a' )
                digitOne -= 'a' -10;
            else
                digitOne -= '0';
            unsigned char digitTwo = [hexStr characterAtIndex: (x * 2) +1];
            if( digitTwo >= 'a' )
                digitTwo -= 'a' -10;
            else
                digitTwo -= '0';
            printf("%01x%01x",digitOne,digitTwo);
            theBytes[x] = (digitOne << 4) | digitTwo;
        }
        printf("\n");

        for( int x = 0; x < sizeof(theBytes); x++ )
            printf("%02x",theBytes[x]);
        printf("\n");
    }
}

Note: This code naïvely assumes that you are providing a correct string. I.e. your input has to consist of lowercase characters and numbers only, and exactly 18 characters. Anything else and you get a wrong result or an exception.

score 0 · Accepted Answer · answered Mar 30 '17 at 08:04

I finally managed to find the answer to my own question. I am posting it here in case it helps someone else.

So I use a method to convert an NSString hex to bytes :

@implementation NSString (HexToBytes)

    - (NSData *)hexToBytes
    {
        NSMutableData   *data = [NSMutableData data];
        int             idx;

        for (idx = 0; idx + 2 <= self.length; idx += 2) {
            NSRange         range = NSMakeRange(idx, 2);
            NSString        *hexStr = [self substringWithRange:range];
            NSScanner       *scanner = [NSScanner scannerWithString:hexStr];
            unsigned int    intValue;
            [scanner scanHexInt:&intValue];
            [data appendBytes:&intValue length:1];
        }

        return data;
    }

@end

And then, I simply use it like that :

NSString *str = @"AA010158AA7D385002";
NSData *databytes = [str hexToBytes];
char *bytePtr = (char *)[databytes bytes];

And I finally get my char array. Hope it helps someone else.

[This](https://stackoverflow.com/a/7500472/865175) helped me instead of this answer. — Iulian Onofrei, Feb 27 '18 at 16:43

Converting NSString to char byte array

4 Answers4