Versioning

Modern Unix systems follow a versioning scheme for libraries. The version number of a library and the version numbers of libraries on which it depends, are encoded in the library. Also the version number is in some way reflected in its name. The GnuWin dynamic libraries (DLL's) follow a similar versioning scheme.

First, the version number is encoded in the library by adding a resource file to it. You can see the version number by right-clicking on the DLL, choosing Properties and then Version. The version number is at the top this tab page as well as in the list of properties below. This version number is the one from the package, and it may consist of 4 parts: the major number, the minor number, the build number, and the revision number; the revision number is sometimes called the QFE (Quick Fix Engineering) number. If one or more of these subnumbers are omitted in the official package version number, then for the GnuWin library they have been added in the following way: the first empty subnumber is set equal to the number of days elapsed between the day the binary has been created and 1 January 2000, and the next empty one is set equal to the number of seconds elapsed since the start of the day on which the binary was created, divided by 2; both are computed with reference to Universal Coordinated Time (GMT). This practice is copied from Microsoft .NET practice, although there the numbers are computed with reference to local time. In fact, any GnuWin binary has this version number encoded.
A program can retrieve the version number by calling the Win32 API function GetFileVersionInfo. Alternatively, DLL's newer than 1 February 2004, support a function DllGetVersion, similar to the Microsoft shell libraries. DllGetVersion is simpler to use than GetFileVersionInfo. See also the example programs:

• GetFileVersionInfo
• DllGetVersion

The major and minor version numbers are also encoded as the major and minor image version numbers in the header of the libraries and executables. They are in bytes 44 - 47 after the PE signature, which is usually in bytes 0x80 - 0x83, so that the version numbers usually are in bytes 0xC3 - 0xC6;  see the PE-Coff specification for more details. These two version numbers can be retrieved with the help of the ImageHelp library functions, in particular GetImageConfigInformation.

Second, a number is attached to the name of the DLL that reflects its LibTool interface version number. The interface of a library is the set of global variables and global functions it exports. It is described by three integers:

• current: The most recent interface number that this library implements.
• revision: The implementation number of the current interface.
• age: The difference between the newest and oldest interfaces that this library implements. In other words, the library implements all the interface numbers in the range from number current - age to current.

The LibTool version number is usually given in the form current:revision:age. This means that:

• If interfaces have been changed or added, but binary compatibility has been preserved, change to current+1:0:age+1
• If binary compatibility has been broken, e.g. due to removed or changed interfaces, change to current+1:0:0
• If the interface is the same as the previous version, change to current:revision+1:age

The GnuWin DLL's follow the Cygwin practice of adding current - age to the name of the DLL. This number is equal to the oldest interface that is still compatible with the latest interface. Usually the LibTool version info is directly set in the Makefile of the library. If no LibTool version info is available, then it is assumed that

• current = major number + build number
• revision = minor number
• age = build number

so that in effect the major number of the package will be added to the name of the library. If current is equal to age, then the version number would be zero, but then it is usually omitted.

You can see the complete LibTool version number by right-clicking on the DLL, choosing Properties and then Version. The LibTool version number is in the box with the list of properties. A program can retrieve this version number by calling the Win32 API function GetFileVersionInfo.