In GNAT a compilation environment is defined by the current directory at the time that a compile command is given. This current directory is searched for a file whose name is gnat.adc. If this file is present, it is expected to contain one or more configuration pragmas that will be applied to the current compilation. However, if the switch -gnatA is used, gnat.adc is not considered.
Configuration pragmas may be entered into the gnat.adc file
either by running gnatchop on a source file that consists only of
configuration pragmas, or more conveniently by
direct editing of the gnat.adc file, which is a standard format
source file.
In addition to gnat.adc, additional files containing configuration pragmas may be applied to the current compilation using the switch -gnatecpath. path must designate an existing file that contains only configuration pragmas. These configuration pragmas are in addition to those found in gnat.adc (provided gnat.adc is present and switch -gnatA is not used).
It is allowed to specify several switches -gnatec, all of which will be taken into account.
If you are using project file, a separate mechanism is provided using project attributes, see Specifying Configuration Pragmas for more details.