I would like to know how to parse a hex string, representing a number, in Objective-C. I am willing to use both an objective, or a C-based method, either is fine.
example:
#01FFFFAB
should parse into the integer:
33554347
Any help would be appreciated!
Joshua Weinberg's answer is mostly correct, however the 0x prefix is optional when scanning hexadecimal integers. If you have a string in the format #01FFFFAB, you can still use NSScanner, but you can skip the first character.
unsigned result = 0;
NSScanner *scanner = [NSScanner scannerWithString:#"#01FFFFAB"];
[scanner setScanLocation:1]; // bypass '#' character
[scanner scanHexInt:&result];
you can use NSScanner for this
unsigned int outVal;
NSScanner* scanner = [NSScanner scannerWithString:#"0x01FFFFAB"];
[scanner scanHexInt:&outVal];
outVal will contain the int you're looking for. The 0x is optional.
strtol() is your friend.
It converts a string to a long, and you can pass the base of the number in. Strip that # sign off first though, or pass to strtol a pointer to the first numerical character.
You can use the below line for conversion. Its just one line code:
NSString *hexString = #"01FFFFAB";
length = (UInt64)strtoull([hexString UTF8String], NULL, 16);
NSLog(#"The required Length is %d", length);
Happy Coding!!!
Swift 4 standard library introduced new initializer for parsing all integer types. It takes string to parse with radix (i.e. base) and returns optional integer:
let number = Int("01FFFFAB", radix: 16)!
According to apple:
An NSScanner object interprets and converts the characters of an
NSString object into number and string values.
so, if u have NSData obj u can do next
NSString *dataDescription = data.description;
NSString *dataAsString = [dataDescription substringWithRange:NSMakeRange(1, [dataDescription length]-2)];
unsigned intData = 0;
NSScanner *scanner = [NSScanner scannerWithString:dataAsString];
[scanner scanHexInt:&intData];
For Swift 3:
var hex = "#01FFFFAB"
hex.remove(at: hex.startIndex)
var rgbValue:UInt32 = 0
Scanner(string: hex).scanHexInt32(&rgbValue)
// rgbValue == 33554347
Related
I have an NSString with octal numbers:
NSString* octal = #"247";
I'd like to convert this to an integer in base 10.
If this were a hex number I could use NSScanner scanHex method, but there is no scanOct...
Thanks!
The standard C library has conversion functions for this purpose:
NSString* octal = #"247";
unsigned long value;
sscanf([octal UTF8String], "%lo", &value);
NSString* decimal = [#(value) stringValue];
decimal now contains the converted base 10 value.
Simple task: I need to convert two characters to two numbers, add them together and change that back to an character.
What I have got: (works perfect in Java - where encoding is handled for you, I guess):
int myChar1 = (int)([myText1 characterAtIndex:i]);
int myChar2 = (int)([myText2 characterAtIndex:keyCurrent]);
int newChar = (myChar1 + myChar2);
//NSLog(#"Int's %d, %d, %d", textChar, keyChar, newChar);
char newC = ((char) newChar);
NSString *tmp1 = [NSString stringWithFormat:#"%c", newC];
NSString *tmp2 = [NSString stringWithFormat:#"%#", newString];
newString = [NSString stringWithFormat:#"%#%#", tmp2, tmp1]; //Adding these char's in a string
The algorithm is perfect, but now I can't figure out how to implement encoding properties. I would like to do everything in UTF-8 but have no idea how to get a char's UTF-8 value, for instance. And if I've got it, how to change that value back to an char.
The NSLog in the code outputs the correct values. But when I try to do the opposite with the algorithm (I.e. - the values) then it goes wrong. It gets the wrong character value for weird/odd characters.
NSString works with unichar characters that are 2 bytes long (16 bits). Char is one byte long so you can only store code point from U+0000 to U+00FF (i.e. Basic Latin and Latin-1 Supplement).
You should do you math on unichar values then use +[NSString stringWithCharacters:length:] to create the string representation.
But there is still an issue with that solution. You code may generate code points between U+D800 and U+DFFF that aren't valid Unicode characters. The standard reserves them to encode code points from U+10000 to U+10FFFF in UTF-16 by pairs of 16-bit code units. In such a case, your string would be ill-formed and could neither be displayed nor converted in UTF8.
Also, the temporary variable tmp2 is useless and you should not create a new newString as you concatenate the string but rather use a NSMutableString.
I am assuming that your strings are NSStrings consisting of numerals which represent a number. If that is the case, you could try the following:
Include the following headers:
#include <inttypes.h>
#include <stdlib.h>
#include <stdio.h>
Then use the following code:
// convert NSString to UTF8 string
const char * utf8String1 = [myText1 UTF8String];
const char * utf8String2 = [myText2 UTF8String];
// convert UTF8 string into long integers
long num1 = strtol(utf8String1, NULL 0);
long num2 = strtol(utf8String2, NULL 0);
// perform calculations
long calc = num1 - num2;
// convert calculated value back into NSString
NSString * calcText = [[NSString alloc] initWithFormat:#"%li" calc];
// convert calculated value back into UTF8 string
char calcUTF8[64];
snprintf(calcUTF8, 64, "%li", calc);
// log results
NSLog(#"calcText: %#", calcText);
NSLog(#"calcUTF8: %s", calcUTF8);
Not sure if this is what you meant, but from what I understood, you wanted to create a NSString with the UTF-8 string encoding from a char?
If that's what you want, maybe you can use the initWithCString:encoding: method in NSString.
I'm working with a database that includes hex codes for UTF32 characters. I would like to take these characters and store them in an NSString. I need to have routines to convert in both ways.
To convert the first character of an NSString to a unicode value, this routine seems to work:
const unsigned char *cs = (const unsigned char *)
[s cStringUsingEncoding:NSUTF32StringEncoding];
uint32_t code = 0;
for ( int i = 3 ; i >= 0 ; i-- ) {
code <<= 8;
code += cs[i];
}
return code;
However, I am unable to do the reverse (i.e. take a single code and convert it into an NSString). I thought I could just do the reverse of what I do above by simply creating a c-string with the UTF32 character in it with the bytes in the correct order, and then create an NSString from that using the correct encoding.
However, converting to / from cstrings does not seem to be reversible for me.
For example, I've tried this code, and the "tmp" string is not equal to the original string "s".
char *cs = [s cStringUsingEncoding:NSUTF32StringEncoding];
NSString *tmp = [NSString stringWithCString:cs encoding:NSUTF32StringEncoding];
Does anyone know what I am doing wrong? Should I be using "wchar_t" for the cstring instead of char *?
Any help is greatly appreciated!
Thanks,
Ron
You have a couple of reasonable options.
1. Conversion
The first is to convert your UTF32 to UTF16 and use those with NSString, as UTF16 is the "native" encoding of NSString. It's not actually all that hard. If the UTF32 character is in the BMP (e.g. it's high two bytes are 0's), you can just cast it to unichar directly. If it's in any other plane, you can convert it to a surrogate pair of UTF16 characters. You can find the rules on the wikipedia page. But a quick (untested) conversion would look like
UTF32Char inputChar = // my UTF-32 character
inputChar -= 0x10000;
unichar highSurrogate = inputChar >> 10; // leave the top 10 bits
highSurrogate += 0xD800;
unichar lowSurrogate = inputChar & 0x3FF; // leave the low 10 bits
lowSurrogate += 0xDC00;
Now you can create an NSString using both characters at the same time:
NSString *str = [NSString stringWithCharacters:(unichar[]){highSurrogate, lowSurrogate} length:2];
To go backwards, you can use [NSString getCharacters:range:] to get the unichar's back and then reverse the surrogate pair algorithm to get your UTF32 character back (any characters which aren't in the range 0xD800-0xDFFF should just be cast to UTF32 directly).
2. Byte buffers
Your other option is to let NSString do the conversion directly without using cStrings. To convert a UTF32 value into an NSString you can use something like the following:
UTF32Char inputChar = // input UTF32 value
inputChar = NSSwapHostIntToLittle(inputChar); // swap to little-endian if necessary
NSString *str = [[[NSString alloc] initWithBytes:&inputChar length:4 encoding:NSUTF32LittleEndianStringEncoding] autorelease];
To get it back out again, you can use
UTF32Char outputChar;
if ([str getBytes:&outputChar maxLength:4 usedLength:NULL encoding:NSUTF32LittleEndianStringEncoding options:0 range:NSMakeRange(0, 1) remainingRange:NULL]) {
outputChar = NSSwapLittleIntToHost(outputChar); // swap back to host endian
// outputChar now has the first UTF32 character
}
There are two probelms here:
1:
The first one is that both [NSString cStringUsingEncoding:] and [NSString getCString:maxLength:encoding:] return the C-string in native-endianness (little) without adding a BOM to it when using NSUTF32StringEncoding and NSUTF16StringEncoding.
The Unicode standard states that: (see, "How I should deal with BOMs")
"If there is no BOM, the text should be interpreted as big-endian."
This is also stated in NSString's documentation: (see, "Interpreting UTF-16-Encoded Data")
"... if the byte order is not otherwise specified, NSString assumes that the UTF-16 characters are big-endian, unless there is a BOM (byte-order mark), in which case the BOM dictates the byte order."
Although they're referring to UTF-16, the same applies to UTF-32.
2:
The second one is that [NSString stringWithCString:encoding:] internally uses CFStringCreateWithCString to create the C-string. The problem with this is that CFStringCreateWithCString only accepts strings using 8-bit encodings. From the documentation: (see, "Parameters" section)
The string must use an 8-bit encoding.
To solve this issue:
Explicitly state the encoding endianness you want to use both ways (NSString -> C-string and C-string -> NSString)
Use [NSString initWithBytes:length:encoding:] when trying to create an NSString from a C-string encoded in UTF-32 or UTF-16.
Hope this helps!
I am used to doing this in C or C++, ie:
myChar++;
should increment a letter.
I am trying to do the same in Objective-C, except that I have a NSString to start off with (the NSString is always just one letter). I have tried converting the NSString to a char *, but this method is deprecated and other ways of achieving this don't seem to work.
How should I convert an NSString to a char * - or, is there a way to increment a character in objective-c without needing a char * somehow?
Thanks :)
// Get the first character as a UTF-16 (2-byte) character:
unichar c = [string characterAtIndex:0];
// Increment as usual:
c++;
// And to turn it into a 1-character string again:
[NSString stringWithCharacters:&c length:1];
Of course, this assumes incrementing a Unicode character makes sense, which does for ASCII-range characters but probably not for others.
How about NSString's
- (unichar)characterAtIndex:(NSUInteger)index;
Would that work?
Say I have a string like "123alpha". I can use NSNumber to get the 123 out, but how can I determine the part of the string that NSNumber didn't use?
You can use NSScanner to both get the value and the rest of the string.
NSString *input = #"123alpha";
NSScanner *scanner = [NSScanner scannerWithString:input];
float number;
[scanner scanFloat:&number];
NSString *rest = [input substringFromIndex:[scanner scanLocation]];
If it is important to know exactly what is left after parsing the value this is a better approach than trying to trim characters. While I can't think of any particular bad input at the moment that would fail the solution suggested by the OP in the comment to this answer, it looks like a bug waiting to happen.
if your numbers are always at the beginning or end of a string and you want only the remaining characters, you could trim with a character set.
NSString *alpha = #"123alpha";
NSString *stripped = [alpha stringByTrimmingCharactersInSet:[NSCharacterSet characterSetWithCharactersInString:#"0123456789"]];
If its starts out as a char * (as opposed to an NSString *), you can use strtol() to get the number and discover where the number ends in a single call.