Hex value in C string - c

I need to prepare constant array of ANSI C strings that contains bytes from range of 0x01 to 0x1a. I made custom codepage, so those values represents different characters (i.e. 0x09 represents Š). I'd like to initialise the array in that way:
static const char* brands[] = {
"Škoda",
//etc...
};
How can I put 0x09 instead of Š in "Škoda"?

Recommend not using "\x09koda", use octal or spaced strings.
The problem is that hexadecimal escape sequences are not limited in their length. So if the next char is a hexadecimal character, problems occur. Use octal, which is limited to 3. Or use separated strings. The compiler will concatenate then, but the escape sequence will not accidentally run too far.
// problematic
"\x09Czech"
^^^^^--- The escape sequence is \x09C, but \0x09 was hoped for
// recommend octal
"\0111234"
^^^^--- The escape sequence is \011
// recommend spaced strings
"\x09" "Czech"

Very simple
"Škoda" -> "\x09koda"

How can I put 0x09 instead of Š in "Škoda"?
"\x09koda"

Have a look at escape squences - i.e \x09
For hex escape you want to use the \Xnnn, for octal just \nnn and for unicode \Unnnn

Related

Separating hexadecimal escape sequences in strings

Can a string constant like "foo" "\x01" "bar" be written as a single string literal (while keeping the hexadecimal notation)? With "foo\x01bar" the escape sequence seems to be interpreted as \x01ba since I get the warning "hex escape sequence out of range."
"foo" "\x01" "bar" is a string literal.
The C standard states that a hexadecimal escape sequence is the longest sequence of characters that can constitute the escape sequence. Without the explicit concatenation (which is the common workaround to this problem), the compiler parses \x01ba which is obviously out of range.
How about "foo\x01\142ar"? Is that cheating?
Another solution is to simply write the escaped character in octal, instead of hexadecimal
"foo\1bar"
and no more ambiguity...

Unknown escape sequence

I am trying to printf a string that shows a temperature table
printf("TABLE 24A (20\°C)");
The degree sign is a constant I have defined as 0xDF so the the string looks like this: "TABLE 24A (20\xDF C)"
This works but looks incorrect because of the space between the \xDF and the C.
If I remove the space the compiler issues a warning hex escape sequence out of range.
If I modify the string to "TABLE 24A (20\xDF\C)" I get the correct result but the compiler issues warning unknown escape sequence: '\C'
Is there a way to get rid of the warnings but lose the space between the two characters?
You can take advantage of the fact that consecutive string literals are automatically concatenated:
printf("**TABLE 24A (20\xDF" "C)**");
This prevents the parser from consuming more characters for the escape sequence than you want.
You could also pass in the character as a parameter and use the %c format specifier to print it:
printf("**TABLE 24A (20%cC)**", '\xDF');
\x escape sequences consume as many adjacent hex digits as possible. The C is being parsed as a hex digit.
With \x, you could combine two adjacent string literals.
printf("**TABLE 24A (20\xDF""C)**");
Or use a \unnnn Unicode escape, which is limited to four hex characters.
printf("**TABLE 24A (20\u00DFC)**");
Or octal \nnn:
printf("**TABLE 24A (20\337C)**");

Check for Special Characters in C

I got some help on how to see if a "string" in C contains a specific character. In short:
if(*s=='x') { //Where x is some character
//Do something
}
Now, as far as I can see, this works for letters in the English alphabet (a-z, A-Z).
However, how can I check if the current character equals a special character (such as æ, ø, or å)?
Just compare to the ASCII code of the character:
if(*s==10) { //Where 10 is the ASCII code of the special character
//Do something
}
You can find your ASCII code here: http://www.asciitable.com/
In most cases you should be using a function for this: strchr for looking for a single byte, or strstr for looking for more than a single byte.
Also, in general C does not know about characters, it only knows about bytes. A special character may be a single byte - æ in iso8859-1 encoding is \xe6, for example - or it may be more than one byte: the same character in utf-8 encoding is the 2-byte sequence \xc3\xa6.
To search a utf-8 encoded string for æ you could use
strstr(s, "\xc3\xa6")
Compare the character to the actual value (as long as the value is between 0 and 255).
See the æ wiki page for particular values. So
if (*s == 0xe6)
for lower case
if (*s == 0xc6)
for upper case

How to write ascii symbol into char table?

Let's assume that I've got such a table:
char *table = "abcdef\n";
How can I put '\n' as decimal subsituide (eg. in hex I put \x0D, in oct I put \015, but what about decimal?)
'/n' is not a character control, but a multi-character constant, so I assume you're talking about '\n' instead.
There is no escape notation in decimal, so simply use \n, the octal (\012 or \12) or the hexadecimal (\x0a) escape notation.
Learn more about escape sequences.
Or you can define one Macro #define NEW_LINE "\n".
then use char *table = "abcdef"NEW_LINE;
And if you cout <<table; out put will be:
abcdef
_
It means the value of table is "abcdef\n"

Convert this kind of hex string to a NSData/NSString

I have this hex string:
\x5c30\x3032\x5f5c\x3337\x345c\x3334\x366f\x5c32\x3633\x5c30\x3136\x5c32\x3132\x5c32\x3234\x4e5c\x3236\x335c\x3231\x335c\x3337\x355c\x3335\x315c\x3232\x365c\x3337
How could I convert it to a NSString or NSData? I though of using C methods, but I'm not experienced in C :(
Looks like Unicode characters (specifically, CJK ideographs) to me.
Use an NSScanner to scan the string. Scan up to a backslash, and add whatever you scanned to a mutable string. Then, scan the backslash and throw it away, and then scan the x and throw that away.
Then, scan four single characters, which will be the digits (NSScanner doesn't have a method to scan a single character, so you will need to get them yourself using characterAtIndex: and then adjust the scanner's scan location accordingly). Perform the appropriate conversion of the hexadecimal digit characters to numbers and the math to assemble a single number from them, and you will have the code point (character value) represented by the escape sequence. Add that single character to your string.
Repeat that until you run out of input string, and you will have converted the input string with all its escape sequences into a string with the unescaped characters.

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