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When using a project file, you can invoke gnatmake with one or several main subprograms, by specifying their source files on the command line.
gnatmake -Pprj main1.adb main2.adb main3.adb
Each of these needs to be a source file of the same project, except when the switch -u is used.
When -u is not used, all the mains need to be sources of the
same project, one of the project in the tree rooted at the project specified
on the command line. The package Builder of this common project, the
"main project" is the one that is considered by gnatmake.
When -u is used, the specified source files may be in projects
imported directly or indirectly by the project specified on the command line.
Note that if such a source file is not part of the project specified on the
command line, the switches found in package Builder of the
project specified on the command line, if any, that are transmitted
to the compiler will still be used, not those found in the project file of
the source file.
When using a project file, you can also invoke gnatmake without
explicitly specifying any main, and the effect depends on whether you have
defined the Main attribute. This attribute has a string list value,
where each element in the list is the name of a source file (the file
extension is optional) that contains a unit that can be a main subprogram.
If the Main attribute is defined in a project file as a non-empty
string list and the switch -u is not used on the command
line, then invoking gnatmake with this project file but without any
main on the command line is equivalent to invoking gnatmake with all
the file names in the Main attribute on the command line.
Example:
project Prj is
for Main use ("main1.adb", "main2.adb", "main3.adb");
end Prj;
With this project file, "gnatmake -Pprj"
is equivalent to
"gnatmake -Pprj main1.adb main2.adb main3.adb".
When the project attribute Main is not specified, or is specified
as an empty string list, or when the switch -u is used on the command
line, then invoking gnatmake with no main on the command line will
result in all immediate sources of the project file being checked, and
potentially recompiled. Depending on the presence of the switch -u,
sources from other project files on which the immediate sources of the main
project file depend are also checked and potentially recompiled. In other
words, the -u switch is applied to all of the immediate sources of the
main project file.
When no main is specified on the command line and attribute Main exists
and includes several mains, or when several mains are specified on the
command line, the default switches in package Builder will
be used for all mains, even if there are specific switches
specified for one or several mains.
But the switches from package Binder or Linker will be
the specific switches for each main, if they are specified.