Replace unicode value in string - iphone

Question

I have a string #"\EOP". I want to dislpay this to user. But when i display this string in textfield, It shows only OP. I tried to print that in console while debugging and it shows ¿OP
So \E is unicode value and that's why it's having some issue of encoding. I can fix this issue by:
NSString *str=[str stringByReplacingOccurrencesOfString:#"\E" withString:#"\\E"];
With this it will display perfect string #"\EOP".
Here my issue is that there can be many more characters same like \E for example \u. How can I implement one fix for all these kind of characters?

Answer 1

\E in the string #"\EOP" is the character with the ASCII-code (or Unicode) 27,
which is a control character.
I don't know of a built-in method to escape all control characters in a string.
The following code uses NSScanner to locate the control characters, and replaces them
using a lookup-table. The control characters are replaced by "Character Escape Codes"
such as "\r" or "\n" if possible, otherwise by "\x" followed by the hex-code.
NSString *str = #"\EOP";
NSCharacterSet *controls = [NSCharacterSet controlCharacterSet];
static char *replacements[] = {
"0", NULL, NULL, NULL, NULL, NULL, NULL, "\\a",
"\\b", "\\t", "\\n", "\\v", "\\f", "\\r", NULL, NULL,
NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
NULL, NULL, NULL, "\\e"};
NSScanner *scanner = [NSScanner scannerWithString:str];
[scanner setCharactersToBeSkipped:nil];
NSMutableString *result = [NSMutableString string];
while (![scanner isAtEnd]) {
NSString *tmp;
// Copy all non-control characters verbatim:
if ([scanner scanUpToCharactersFromSet:controls intoString:&tmp]) {
[result appendString:tmp];
}
if ([scanner isAtEnd])
break;
// Escape all control characters:
if ([scanner scanCharactersFromSet:controls intoString:&tmp]) {
for (int i = 0; i < [tmp length]; i++) {
unichar c = [tmp characterAtIndex:i];
char *r;
if (c < sizeof(replacements)/sizeof(replacements[0])
&& (r = replacements[c]) != NULL) {
// Replace by well-known character escape code:
[result appendString:#(r)];
} else {
// Replace by \x<hexcode>:
[result appendFormat:#"\\x%02x", c];
}
}
}
}
NSLog(#"%#", result);

Answer 2

You can always replace \ with \\. These are called Escape Sequences.
Sample Code :
NSString *str = #"\EOP";
NSString *myNewStr = [str stringByReplacingOccurrencesOfString:#"\\" withString:#"\\\\"];
NSLog(#"myNewStr :: %#",myNewStr);

Answer 3

If you want a backslash (\) to appear in a string literal, you need to escape it in the string literal i.e.
NSString* foo = #"\\EOP";
The above will give you the Unicode sequence 5C 45 4F 50 which is what you want.