Using the gnatprep Command (with examples)

Use Case 1: Use symbol definitions from a file

Code:

gnatprep source_file target_file definitions_file

Motivation:

The gnatprep command allows us to use symbol definitions from a file when preprocessing Ada source code files. This can be useful when we want to have different versions of the source code depending on the specific symbols defined.

Explanation:

• source_file: The path to the source file that needs to be preprocessed.
• target_file: The path to the output file where the preprocessed content will be saved.
• definitions_file: The path to the file that contains the symbol definitions. This file should have one definition per line, in the format “name=value”, where “name” is the symbol name and “value” is its corresponding value.

Example Output:

Assuming we have a source file called my_code.adb with the following content:

with Ada.Text_IO;

procedure My_Code is
begin
   -- This is a preprocessed statement
   -- ${EXAMPLE_MESSAGE}
   Ada.Text_IO.Put("Hello, World!");
end My_Code;

And we have a definitions file called definitions.txt with the following content:

EXAMPLE_MESSAGE="This is a preprocessed message"

Running the following command:

gnatprep my_code.adb preprocessed_code.adb definitions.txt

Will preprocess the my_code.adb file using the symbol definition from definitions.txt file and generate a new file called preprocessed_code.adb with the following content:

with Ada.Text_IO;

procedure My_Code is
begin
   -- This is a preprocessed statement
   -- "This is a preprocessed message"
   Ada.Text_IO.Put("Hello, World!");
end My_Code;

Use Case 2: Specify symbol values in the command-line

Code:

gnatprep -Dname=value source_file target_file

Motivation:

The second use case of the gnatprep command allows us to specify symbol values directly in the command-line. This can be useful when we want to override the default symbol definitions or provide different values for different preprocessing scenarios.

Explanation:

• -Dname=value: This option allows us to specify symbol names and their corresponding values directly in the command-line. Multiple symbol definitions can be provided by separating them with spaces.

Example Output:

Using the same my_code.adb file as in the previous example, running the following command:

gnatprep -DEXAMPLE_MESSAGE="This is a preprocessed message" my_code.adb preprocessed_code.adb

Will preprocess the my_code.adb file using the symbol definition specified in the command-line and generate a new file called preprocessed_code.adb with the following content:

with Ada.Text_IO;

procedure My_Code is
begin
   -- This is a preprocessed statement
   -- "This is a preprocessed message"
   Ada.Text_IO.Put("Hello, World!");
end My_Code;

Note that in this case, the symbol definition from the definitions.txt file is not used because we provided a directly in the command-line.

Conclusion

Using the gnatprep command, we can preprocess Ada source code files by utilizing symbol definitions from a file or specifying symbol values directly in the command-line. These features enable us to have flexible code generation based on different symbol definitions, making our development process more efficient and adaptable.