(Objective-C) Determine File Type from Binary Content of File

Note: This example requires Chilkat v9.5.0.64 or later.

Many file types have "signatures" (leading bytes) that signify the type of file. It allows for programs to identify the likely type of file given the first few bytes contained within the file. This example shows how to identify a few common types files. For other file types, you can do a short bit of investigative work by examining the first few bytes of an sample file, and searching the Internet for information about the file type. Use this same technique for handling other file types that have leading "signature" bytes.

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#import <CkoFileAccess.h>
#import <CkoBinData.h>

// Note: This example requires Chilkat v9.5.0.64 or later.

// To identify a file by the first few bytes, we'll load a few bytes from the start
// of the file, and then examine the bytes as both hex and quoted-printable.

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

// A JPG file.
CkoBinData *jpgData = [[CkoBinData alloc] init];
[fac OpenForRead: @"qa_data/jpg/starfish.jpg"];
// The the first 8 bytes of the JPG file.
[fac FileReadBd: [NSNumber numberWithInt: 8] binData: jpgData];
[fac FileClose];

// JPG hex: FFD8FFE000104A46
// JPG qp: =FF=D8=FF=E0=00=10JF
NSLog(@"%@%@",@"JPG hex: ",[jpgData GetEncoded: @"hex"]);
NSLog(@"%@%@",@"JPG qp: ",[jpgData GetEncoded: @"qp"]);

// A JPG begins with the following two bytes: 0xFF, 0xD8
// Your program can check to see if the hex string begins with "FFD8", or if the qp string begins with "=FF=D8".

// ----------------------------------------
// A PNG file.
CkoBinData *pngData = [[CkoBinData alloc] init];
[fac OpenForRead: @"qa_data/png/anemone.png"];
// The the first 8 bytes of the PNG file.
[fac FileReadBd: [NSNumber numberWithInt: 8] binData: pngData];
[fac FileClose];

// PNG hex: 89504E470D0A1A0A
// PNG qp: =89PNG=1A=0A
NSLog(@"%@%@",@"PNG hex: ",[pngData GetEncoded: @"hex"]);
NSLog(@"%@%@",@"PNG qp: ",[pngData GetEncoded: @"qp"]);
// A PNG file begins with the byte 0x89, followed by the us-ascii bytes "PNG".

// ----------------------------------------
// A PDF file.
CkoBinData *pdfData = [[CkoBinData alloc] init];
[fac OpenForRead: @"qa_data/pdf/fishing.pdf"];
// The the first 8 bytes of the PDF file.
[fac FileReadBd: [NSNumber numberWithInt: 8] binData: pdfData];
[fac FileClose];

// PDF hex: 255044462D312E33
// PDF qp: %PDF-1.3
NSLog(@"%@%@",@"PDF hex: ",[pdfData GetEncoded: @"hex"]);
NSLog(@"%@%@",@"PDF qp: ",[pdfData GetEncoded: @"qp"]);
// A PDF file begins with the us-ascii chars "%PDF"

// ----------------------------------------
// A Zip file.
CkoBinData *zipData = [[CkoBinData alloc] init];
[fac OpenForRead: @"qa_data/zips/test.zip"];
// The the first 8 bytes of the Zip file.
[fac FileReadBd: [NSNumber numberWithInt: 8] binData: zipData];
[fac FileClose];

// PDF hex: 504B030414000000
// PDF qp: PK=03=04=14=00=00=00
NSLog(@"%@%@",@"PDF hex: ",[zipData GetEncoded: @"hex"]);
NSLog(@"%@%@",@"PDF qp: ",[zipData GetEncoded: @"qp"]);
// A Zip archive begins with the us-ascii chars "PK" followed by the bytes 0x03, 0x04.