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24 Version Information

Compile-time and run-time version checks.

24.1 Overview

Cairo has a three-part version number scheme. In this scheme, we use even vs. odd numbers to distinguish fixed points in the software vs. in-progress development, (such as from git instead of a tar file, or as a "snapshot" tar file as opposed to a "release" tar file).

     
      _____ Major. Always 1, until we invent a new scheme.
     /  ___ Minor. Even/Odd = Release/Snapshot (tar files) or Branch/Head (git)
     | /  _ Micro. Even/Odd = Tar-file/git
     | | /
     1.0.0

Here are a few examples of versions that one might see.

     
     Releases
     --------
     1.0.0 - A major release
     1.0.2 - A subsequent maintenance release
     1.2.0 - Another major release
     
     Snapshots
     ---------
     1.1.2 - A snapshot (working toward the 1.2.0 release)
     
     In-progress development (eg. from git)
     --------------------------------------
     1.0.1 - Development on a maintenance branch (toward 1.0.2 release)
     1.1.1 - Development on head (toward 1.1.2 snapshot and 1.2.0 release)

24.2 Compatibility

The API/ABI compatibility guarantees for various versions are as follows. First, let's assume some cairo-using application code that is successfully using the API/ABI "from" one version of cairo. Then let's ask the question whether this same code can be moved "to" the API/ABI of another version of cairo.

Moving from a release to any later version (release, snapshot, development) is always guaranteed to provide compatibility.

Moving from a snapshot to any later version is not guaranteed to provide compatibility, since snapshots may introduce new API that ends up being removed before the next release.

Moving from an in-development version (odd micro component) to any later version is not guaranteed to provide compatibility. In fact, there's not even a guarantee that the code will even continue to work with the same in-development version number. This is because these numbers don't correspond to any fixed state of the software, but rather the many states between snapshots and releases.

24.3 Examining the version

Cairo provides the ability to examine the version at either compile-time or run-time and in both a human-readable form as well as an encoded form suitable for direct comparison. Cairo also provides the macro cairo-version-encode to perform the encoding.

     
     Compile-time
     ------------
     CAIRO_VERSION_STRING    Human-readable
     CAIRO_VERSION           Encoded, suitable for comparison
     
     Run-time
     --------
     cairo_version_string()  Human-readable
     cairo_version()         Encoded, suitable for comparison

For example, checking that the cairo version is greater than or equal to 1.0.0 could be achieved at compile-time or run-time as follows:

     
     ##if CAIRO_VERSION >= CAIRO_VERSION_ENCODE(1, 0, 0)
     printf ("Compiling with suitable cairo version: %s\n", %CAIRO_VERSION_STRING);
     ##endif
     
     if (cairo_version() >= CAIRO_VERSION_ENCODE(1, 0, 0))
         printf ("Running with suitable cairo version: %s\n", cairo_version_string ());

24.4 Usage

— Function: cairo-version ⇒  (ret <int>)

Returns the version of the cairo library encoded in a single integer as per ‘CAIRO_VERSION_ENCODE’. The encoding ensures that later versions compare greater than earlier versions.

A run-time comparison to check that cairo's version is greater than or equal to version X.Y.Z could be performed as follows:

          
          if (cairo_version() >= CAIRO_VERSION_ENCODE(X,Y,Z)) {...}

See also cairo-version-string as well as the compile-time equivalents ‘CAIRO_VERSION’ and ‘CAIRO_VERSION_STRING’.

ret
the encoded version.
— Function: cairo-version-string ⇒  (ret <char >)

Returns the version of the cairo library as a human-readable string of the form "X.Y.Z".

See also cairo-version as well as the compile-time equivalents ‘CAIRO_VERSION_STRING’ and ‘CAIRO_VERSION’.

ret
a string containing the version.