How to store a version number in a static library?

Question

How can I store a version number in a static library (file.a) and later check for its version in Linux?

P.S. I need possibility to check version of file any time without any special executable using only by shell utilities.

Answer 1

Maybe you could create a string with the version like this:

char* library_version = { "Version: 1.3.6" };

and to be able to check it from the shell just use:

strings library.a | grep Version | cut -d " " -f 2

Answer 2

In addition to providing a static string as mentioned by Puppe, it is common practice to provide a macro to retrieve the version check for compatibility. For example, you could have the following macros (declared in a header file to be used with your library):

#define MYLIB_MAJOR_VERSION 1
#define MYLIB_MINOR_VERSION 2
#define MYLIB_REVISION 3
#define MYLIB_VERSION "1.2.3"
#define MYLIB_VERSION_CHECK(maj, min) ((maj==MYLIB_MAJOR_VERSION) && (min<=MYLIB_MINOR_VERSION))

Notice with the MYLIB_CHECK_VERSION macro, I'm assuming you want a specific major rev and a minor rev greater than or equal to your desired version. Change as required for your application.

Then use it from a calling application, something like:

if (! MYLIB_VERSION_CHECK(1, 2)) {
    fprintf(stderr, "ERROR: incompatible library version\n");
    exit(-1);
}

This approach will cause the version information to come from the included header file. Additionally, it will be optimized at compile time for the calling application. With a little more work, you can extract it from the library itself. Read on...

You can also use this information to create a static string stored inside your library, as mentioned by Puppe. Place something like this inside your library:

struct {
    const char* string;
    const unsigned major;
    const unsigned minor;
    const unsigned revision;
} mylib_version = {
    MYLIB_VERSION, MYLIB_MAJOR_VERSION, MYLIB_MINOR_VERSION, MYLIB_REVISION
};

This will create a struct called mylib_version in your library. You can use this to do further verifications by creating functions inside your library and accessing those from a calling application, etc.