Objective-C

Decompress Large Text File in Blocks

See more Compression Examples

Decompresses a large text file in blocks, and compares the restored (decompressed) file with the original to make sure it's correct. Objective-C

#import <CkoCompression.h>
#import <CkoFileAccess.h>
#import <NSString.h>

BOOL success = NO;

// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// First, let's compress a text file.
// We'll then decompress in blocks, and compare the decompressed with the original file.

// Compress a text file:
CkoCompression *compress = [[CkoCompression alloc] init];
compress.Algorithm = @"deflate";

success = [compress CompressFile: @"qa_data/hamlet.xml" destPath: @"qa_data/hamlet_compressed.dat"];
if (success == NO) {
    NSLog(@"%@",compress.LastErrorText);
    return;
}

CkoFileAccess *fac = [[CkoFileAccess alloc] init];

// Examine the uncompressed and compressed sizes:
NSString *originalPath = @"qa_data/hamlet.xml";
// Note: The FileSize method returns a signed 32-bit integer.  If the file is potentially larger than 2GB, call FileSizeStr instead to return
// the size of the file as a string, then convert to an integer value.
NSLog(@"%@%d",@"uncompressed size: ",[[fac FileSize: originalPath] intValue]);
NSLog(@"%@%d",@"compressed size: ",[[fac FileSize: @"qa_data/hamlet_compressed.dat"] intValue]);

// Decompress in blocks..
CkoFileAccess *facSrc = [[CkoFileAccess alloc] init];
CkoFileAccess *facDest = [[CkoFileAccess alloc] init];

[facSrc OpenForRead: @"qa_data/hamlet_compressed.dat"];

// If we compress in 32K chunks, find out how many blocks there will be.
int blockSize = 32768;
int numBlocks = [[facSrc GetNumBlocks: [NSNumber numberWithInt: blockSize]] intValue];

// Open an output file for the decompressed data.
NSString *restoredPath = @"qa_output/hamlet_restored.xml";
success = [facDest OpenForWrite: restoredPath];
if (success == NO) {
    NSLog(@"%@",facDest.LastErrorText);
    return;
}

NSString *decompressedStr = 0;
NSData compressedBytes;

// Assuming numBlocks > 1
compress.FirstChunk = YES;
compress.LastChunk = NO;

int i = 0;
while (i < numBlocks) {
    compressedBytes = [facSrc ReadBlock: [NSNumber numberWithInt: i] blockSize: [NSNumber numberWithInt: blockSize]];
    decompressedStr = [compress DecompressString: compressedBytes];

    [facDest AppendText: decompressedStr charset: @"utf-8"];

    i = i + 1;

    compress.FirstChunk = NO;
    if (i == (numBlocks - 1)) {
        compress.LastChunk = YES;
    }

}

[facSrc FileClose];
[facDest FileClose];

// Examine the size of the restored file.
NSLog(@"%@%d",@"restored size: ",[[fac FileSize: restoredPath] intValue]);

// Compare the contents of the original with the restored.
BOOL bEqualContents = [fac FileContentsEqual: restoredPath path2: originalPath];
NSLog(@"%@%d",@"Contents Equal: ",bEqualContents);