Search a value in a comma separated value file

Question

Hi I have implemented the following method for searching a value in a csv file:

- (void)recordsForValue:(NSString*)searchedValue {


NSAutoreleasePool *pool = [[NSAutoreleasePool alloc]init];

NSError*  err;

    NSString *csvFilePath = //path of csv file
    NSString *csvString = nil;
    csvString = [[NSString alloc]initWithContentsOfFile:csvFilePath encoding:NSASCIIStringEncoding error:&err];
    csvFilePath = nil;
    NSRange searchRange = NSMakeRange(0,csvString.length);
    NSRange foundRange;
    int i=0;

    locationRecordsArray = [NSMutableArray array];

    while (searchRange.location <= csvString.length) {
        NSString *sFinalResult = nil;

        searchRange.length = csvString.length-searchRange.location;
        foundRange = [csvString rangeOfString:searchedValue options:NSCaseInsensitiveSearch range:searchRange];
        if (foundRange.location != NSNotFound) {
            i++;

            NSRange endDivRange;
            NSRange startRange;

            endDivRange.location = foundRange.length + foundRange.location;
            endDivRange.length   = [csvString length] - endDivRange.location;
            endDivRange = [csvString rangeOfString:@"\n" options:NSCaseInsensitiveSearch range:endDivRange];

            if (endDivRange.location != NSNotFound)
            {
                // Tags found: retrieve string between them
                foundRange.location += foundRange.length;
                foundRange.length = endDivRange.location - foundRange.location;
            }

            startRange.location = 0;
            startRange.length = foundRange.location;
            NSString* sTemp = nil;
            sTemp = [[NSString alloc]initWithString:[csvString substringWithRange:startRange]];

            startRange = [sTemp rangeOfString:@"\n" options:NSBackwardsSearch range:startRange];
            [sTemp release];
            if (startRange.location != NSNotFound)
            {
                // Tags found: retrieve string between them
                foundRange.location = startRange.location;
                foundRange.length =   endDivRange.location - foundRange.location;

                sFinalResult = nil;
                sFinalResult = [[NSString alloc]initWithString:[csvString substringWithRange:foundRange]];
                if(sFinalResult != nil)
                    [locationRecordsArray addObject:sFinalResult];
                [sFinalResult release];

            }

            // found an occurrence of the substring! do stuff here
            searchRange.location = foundRange.location+foundRange.length;
        } else {
            // no more substring to find
            break;
        }
    }
    [csvString release];


    [self insertLocationRecordsInDatabase]; // insert records of locationArray

[self performSelectorOnMainThread:@selector(showScanningView) withObject:nil waitUntilDone:NO];
[pool drain];
}

1.The above method is called in a separate thread, so we have to process it in a separate autorelease pool.

2. The 'searchedValue' is a value to be searched in the CSV file string.

3. Whenever we get a location for the value searched in the csvString, we add the complete line of string in an array.The line
is extracted by searching for newline (i.e \n) character.
4. This code is running fine if the length of csvString is small. But in case of a very large csvString, the app is crashing with low
memory warning. I checked in Instruments. The problem is with some
String variable which is reaching the size of 100s of MB and the app
is closing because of low memory.But I am not able to solve how to
optimise the memory of my string variables.Please give some
solution.

Answer 1

Finally my problem solved!! I used the following code to optimise the memory:

- (void)recordsForLocationValue:(NSString*) searchedValue
 {

    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc]init];

    NSError*  err;

         NSString *csvFilePath = //path of csv file
        NSMutableString *csvString = [NSMutableString stringWithContentsOfFile:csvFilePath encoding:NSASCIIStringEncoding error:&err];
        csvFilePath = nil;
        NSRange searchRange = NSMakeRange(0,csvString.length);
        NSRange foundRange;
        int i=0;
        NSString* sTemp = nil;

        locationRecordsArray = [[NSMutableArray alloc]init];

        while ([csvString length] > 1) {

            searchRange.length = csvString.length-searchRange.location;
            foundRange = [csvString rangeOfString: searchedValue
 options:NSCaseInsensitiveSearch range:searchRange];
            if (foundRange.location != NSNotFound) {
                i++;

                NSRange endDivRange;
                NSRange startRange;

                endDivRange.location = foundRange.length + foundRange.location;
                endDivRange.length   = [csvString length] - endDivRange.location;
                endDivRange = [csvString rangeOfString:@"\n" options:NSCaseInsensitiveSearch range:endDivRange];

                if (endDivRange.location != NSNotFound)
                {
                    // Tags found: retrieve string between them
                    foundRange.location += foundRange.length;
                    foundRange.length = endDivRange.location - foundRange.location;
                }

                startRange.location = 0;
                startRange.length = foundRange.location;
                sTemp = [csvString substringWithRange:startRange];
                startRange = [sTemp rangeOfString:@"\n" options:NSBackwardsSearch range:startRange];
                if (startRange.location != NSNotFound)
                {
                    // Tags found: retrieve string between them
                    foundRange.location = startRange.location;
                    foundRange.length =   endDivRange.location - foundRange.location;

                    sTemp = [csvString substringWithRange:foundRange];
                    if(sTemp != nil)
                        [locationRecordsArray addObject:sTemp];
                }

                // found an occurrence of the substring! do stuff here
                searchRange.location = foundRange.location+foundRange.length;

                [csvString deleteCharactersInRange:NSMakeRange(0, searchRange.location-1)];

                searchRange.location = 0;
            }
            else {
                NSLog(@"no more substring to find");

                // no more substring to find
                break;
            }
        }


        [self insertLocationRecordsInDatabase];

    [self performSelectorOnMainThread:@selector(showScanningView) withObject:nil waitUntilDone:NO];
    [pool drain];
    [NSThread exit];
}

Answer 2

use a memory mapping so you dont have to load everything at once.
see: Substitute for NSData deprecated dataWithContentsOfMappedFile

OR

split the file into several smaller files