Objective C - Split NSString into Array, max count - objective-c

Question

I am new to Objective-C, so I am trying to split an String into an Array in this format:
NSString *str = #":49:DE:Bahnhofsstr:12:39:11";
NSArray *arr = [str componentsSeparatedByString:#":"];
I receive the following objects in arr:
[#"", #"49", #"DE", #"Bahnhofsstr", #"12", #"39", #"11"]
But I need it in this format:
[#"", #"49", #"DE", #"Bahnhofsstr:12:39:11"]
Anyone have any ideas?

Answer 1

You can use a regular expression. The one you want is this:
^([^:]*):([^:]*):([^:]*):(.*)$
The above matches three sequences of characters without colons in separated by colons and then a fourth group consisting of any kind of character. The ^ at the front and the $ at the end match the beginning and the end of the string respectively otherwise nonsense like 1:2:3:4:49:DE:Bahnhofsstr:12:39:11 would match because there is a match embedded in the string.
The parenthesis delimit capture groups which will be returned to you once the regular expression matching has been done. The first capture group is all the characters up to the first colon. The second capture group is all the characters between the first and second colons. The third capture group is all the characters between the second and third colons and the fourth capture group is all the characters after the third colon.
There is also a zeroth capture group which is the entire matching sequence.
Here's how to use this in Objective-C:
NSString* pattern = #"^([^:]*):([^:]*):([^:]*):(.*)$";
NSString* line = #":49:DE:Bahnhofsstr:12:39:11";
NSRegularExpression* regex = [NSRegularExpression regularExpressionWithPattern: pattern
options: 0
error: &error];
if (regex == nil)
{
NSLog(#"Invalid regular expression %#, %#", pattern, error);
}
else
{
NSArray* matches = [regex matchesInString: line
options: 0
range: NSMakeRange(0, [line length])];
if ([matches count] == 1)
{
// Should only be one match
NSTextCheckingResult* result = [matches objectAtIndex: 0];
NSMutableArray* captureGroups = [[NSMutableArray alloc] init];
// Omit capture group 0 because it will be the whole string
for (int i = 1 ; i < [result numberOfRanges] ; i++)
{
NSRange groupRange = [result rangeAtIndex: i];
NSString* captureGroup = [line substringWithRange: groupRange];
[captureGroups addObject: captureGroup];
}
NSLog(#"The fields are %#", captureGroups);
}
else
{
// match error
}
}

Answer 2

Regular expressions, as proposed by JeremyP, are an obvious solution to this sort of problem.
Some people don't like regexes, though, so another solution is to use NSScanner which is also made to scan strings and read the result into variables. Given that the delimiter is the same for all fields, it even lends itself to use a nice loop, reducing the tedious scanning code.
Here is an example:
NSString *str = #":49:DE:Bahnhofsstr:12:39:11";
const NSUInteger nFields = 4;
NSScanner *myScanner = [NSScanner scannerWithString: str];
NSMutableArray *arr = [NSMutableArray array];
for (NSUInteger i = 0; i < nFields - 1; i++) {
NSString *field;
// The BOOLs here really ought to be checked
BOOL found = [myScanner scanUpToString: #":" intoString: &field];
BOOL passedDelimiter = [myScanner scanString: #":" intoString: NULL];
[arr addObject: field ?: #"" ];
}
NSString *lastField = [[myScanner string] substringFromIndex:[myScanner scanLocation]];
[arr addObject: lastField];
That last line to read the remainder of the string is taken straight from the docs for NSScanner.