How to compress a directory with libbz2 in C++

Question

I need to create a tarball of a directory and then compress it with bz2 in C++. Is there any decent tutorial on using libtar and libbz2?

Answer 1

Okay, I worked up a quick example for you. No error checking and various arbitrary decisions, but it works. libbzip2 has fairly good web documentation. libtar, not so much, but there are manpages in the package, an example, and a documented header file. The below can be built with g++ C++TarBz2.cpp -ltar -lbz2 -o C++TarBz2.exe:

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <libtar.h>
#include <bzlib.h>
#include <unistd.h>

int main()
{
    TAR *pTar;
    char tarFilename[] = "file.tar";
    char srcDir[] = "dirToZip/";
    char extractTo[] = ".";
    
    tar_open(&pTar, tarFilename, NULL, O_WRONLY | O_CREAT, 0644, TAR_GNU);
    tar_append_tree(pTar, srcDir, extractTo);
    
    close(tar_fd(pTar));

    int tarFD = open(tarFilename, O_RDONLY);

    char tbz2Filename[] =  "file.tar.bz2";
    FILE *tbz2File = fopen(tbz2Filename, "wb");
    int bzError;
    const int BLOCK_MULTIPLIER = 7;
    BZFILE *pBz = BZ2_bzWriteOpen(&bzError, tbz2File, BLOCK_MULTIPLIER, 0, 0);
   
    const int BUF_SIZE = 10000;
    char* buf = new char[BUF_SIZE];
    ssize_t bytesRead;
    while((bytesRead = read(tarFD, buf, BUF_SIZE)) > 0) {
        BZ2_bzWrite(&bzError, pBz, buf, bytesRead);
    }        
    BZ2_bzWriteClose(&bzError, pBz, 0, NULL, NULL);
    close(tarFD);
    remove(tarFilename);

    delete[] buf;

}

Answer 2

Assuming this isn't just a "how can I do this" question, then the obvious way is to fork/exec GNU tar to do it for you. The easiest way is with the system(3) library routine:

  system("/path/to/gtar cfj tarballname.tar.bz2 dirname");

According to this, there are example programs in the libtar disty.

Bzip's documentation includes a section on programming with libbz2.