CODEWITHSUNDEEP
c++installationcross-platform
Will03uk
Will03uk

Reputation: 3444

Embedding compressed files into a c++ program

I want to create a cross-platform installer, in c++. It can be any compression type, eg zip or gzip, embedded inside the program itself like an average installer. I don't want to create many changes on different platforms, linux and windows. How do I embed and extract files to a c++ program, cross-platform?

Upvotes: 0

Views: 1263

Answers (3)

Ben Voigt
Ben Voigt

Reputation: 283733

C++ is a poor choice for a cross-platform installer, because there's no such thing as cross-platform machine code.

C++ code can be extremely portable, but it needs to be compiled for each platform, and then you get a distinct output executable for each platform.

If you want to build installers for many platforms from a single source file, you can use C++. But if you want to build ONE installer that works on many platforms, you'll need to use an interpreted or JIT-compiled language with runtime support available on all your targets. Of those, the only one likely to already be installed on a majority of computers of each platform is Java.

Ok, assuming that you're building many single-platform installers from machine code, this is what is needed:

You need to get the compressed code into the program. You want to do this in a way that doesn't affect the load time badly, nor cause compilation to take a few months. So using an initialized global array is a bad idea.

One way is to link your data in as an additional section. There are tools to help with that, e.g. Binary to COFF converter, I've seen an ELF version as well, maybe this. But this might still cause the runtime library to try to lead the entire file into memory before execution begins.

Another way is to use platform-specific resource APIs. This is efficient, but platform specific.

The most straightforward solution is to simply append the compressed archive to your executable, then append eight more bytes with the file offset where the compressed archive begins. Unpacking is then as simple as opening the executable in read-only mode, fseek(-8, SEEK_END), reading the correct offset, then seeking to the beginning of the compressed data and passing that stream to your decompressor.

Of course, now I find a website listing pretty much the same methods.

And here's a program which implements the last option, with additional ability to store multiple files. I wouldn't recommend doing that, let the compression library take care of storing the file metadata.

Upvotes: 2

PAntoine
PAntoine

Reputation: 689

Use zlib.

Have your packing program generate a list of exe's in the program. i,e.

unsigned char x86_windows_version[] = { 0xff,...,0xff};
unsigned char arm_linux_version[] = { 0xff,...,0xff};

unsigned char* binary_files[MAX_BINARIES] = {x86_windows_version,arm_linux_version};

somewhere in your excitable:

enflate(x86_windows_version);

And thats about it. Look at the zlib docs for the parameters for enflate() and deflate() and that's about it.

It's a pattern used a lot on embedded platforms (that are not linux) mostly for string _tables and other image binaries. It should work for your needs.

Upvotes: 0

James Kanze
James Kanze

Reputation: 153977

The only way I know of to portably embed data (strings or raw, binary data) in a C++ program is to convert it into a data table, then compile that. For raw data, this would look something like:

unsigned char data[] =
{
    //  raw data here.
};

It should be fairly trivial to write a small program which reads your binary data, and writes it out as a C++ table, like the above. Compile it, and link it into your program, and there you are.

Upvotes: 0

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