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When a developer wants to link his program against a third party library, he must know some details about it, specially all flags that need to be passed to the compiler to get a successful link. These may vary depending on the system (i.e., shared or static libraries), on the library version, etc.. There are several solutions to this problem: a configuration script, which gives the proper flags at runtime (this has been used for lots of libraries but is becoming deprecated); a pkgconfig file (mostly used by GNOME), which provides a small database of flags accessed through a common interface; and the Buildtool approach, a pkgflags file, which has the same funcionality as pkgconfig.
Although the native format for package flags in Buildtool is pkgflags, it also supports pkgconfig files for compatibility and interoperability.
To write your configuration scripts, you can get library flags using any of the three approaches described above, specially using the bt_check_pkgflags function (see Section 11.7.6.4, “Package flags”) or the pkgconfig.subr module (see Section 11.8.1, “The pkgconfig module”). Note that the later is discourgaged, as the bt_check_pkgflags function also supports pkgconfig files, and avoids a build dependancy on an external package.
Even though, when you write your own library, it is suggested that you provide pkgflags files (no extra programs needed as this is entirely handled by Buildtool itself). They store package information, like its name or its version and also all the flags needed to compile and link an application against it.
buildtool pkgflags [ -c | --cflags ] [ -h | --help ] [ -l | --libs ] pkgname,[operator,version]...
The bt_pkgflags module is used to get package flags from installed pkgflags files, which are printed to standard output. Each argument specifies a package name from which flags are requested. If the argument contains three fields instead of only one (separated either by commas or spaces), the second is treated as the version operator and the third as the version number. The operator specifies the relation between the installed version and the given one, and it can be one of the following: lt or < for less; le or <= for less or equal; eq or = for equal; ne or != for not equal; ge or >= for greater or equal; gt or > for greater.
The following options are recognized:
-c | -cflags
Requests the list of compiler flags from the given packages.
-h | --help
Shows a short help message, listing all available options and the command syntax.
-l | --libs
Requests the list of linker flags from the given packages.
The following examples could print compiler flags for the foobar library, requesting at least its 2.5 version:
$ buildtool pkgflags -c foobar,ge,2.5 $ buildtool pkgflags -c "foobar >= 2.5"
Pkgflags files are very easily written and parsed. They are plain shell script files that define specific variables, which are:
The name of the package where the pkgflags file comes from.
A short comment about the pkgflags file, usually matches the package's comment.
The version of the library.
The list of compiler flags.
The list of linker flags.
Furthermore, most of the information required in these files can be filled in automatically by the configuration script, using the bt_generate_output function (see Section 11.5.1, “Generating output files”). Here is an example pkgflags file for our foobar library, containing magic strings that will be automatically completed:
BT_PREFIX="@BT_PREFIX@"
BT_DIR_LIB="@BT_DIR_LIB@"
BT_DIR_INCLUDE="@BT_DIR_INCLUDE@"
bpf_name="@BT_PKG_NAME@"
bpf_descr="@BT_PKG_COMMENT@"
bpf_version="@BT_PKG_VERSION@"
bpf_libs="-L${BT_DIR_LIB} -lfoobar"
bpf_cflags="-I${BT_DIR_INCLUDE}"
This file could be stored as data/foobar.bpf.in inside your package. To generate the real pkgflags file, containing the right information, you could add the following target definition to your data/Logic.bt script:
target_foobar.bpf() {
BT_TYPE=output
}
target_foobar.bpf_install() {
bt_install_dir ${BT_DIR_PKGFLAGS}
bt_install_data foobar.bpf ${BT_DIR_PKGFLAGS}
}
Also remember that you will need a call to the bt_generate_output function (Section 11.5.1, “Generating output files”) in your configuration script.