sppu-te-comp-content/SystemsProgrammingAndOperatingSystem
sppu-te-comp-content/SystemsProgrammingAndOperatingSystem
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Added explanation for A3 (dll) code.

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Codes/Group A/Assignment-A3/EXPLANATION.md Normal file
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# Explanation
Please note the files referred in this guide:
- [A3.java]
- [A3.c]
- We're using Java for writing the main program.
- To demonstrate Dynamic Linking Library (DLL) in Java, we'll be declaring functions in Java and implementing them in C (can be C/C++).
- First, we create a Java program `A3.java`,
- This is the main Java file containing function definition and the main function.
- Functions (add, sub, mul, div) in `A3` class in this file are native functions, meaning their body is written in C/C++ in a different file.
- After creating this file, you need to compile it. To do so, run `javac A3.java` (assuming you're already in the directory that contains this file).
- Now, we will generate the header file. For this, run `javac -h A3.java`.
- There will be a new file called `A3.h` in your current working directory,
- This is the header file.
- It contains signatures for native functions we created in the Java file.
- Thus, there's **no need to memorized `A3.c` file** since the functions defined in that file can be found in the header file.
- Create a new `A3.c` file which is the C program file containing function definitions (for add, sub, mul, div)
- Define all the functions (add, sub, mul, div)
- Then, we have to compile the C program file, i.e. `A3.c`. For this, run `gcc -shared -o libA3.so -fPIC -I"$JAVA_HOME/include" -I"$JAVA_HOME/include/linux" A3.c`,
- `gcc` -> GNU compiler for C program
- `-shared` -> tells the compiler to create a shared file (.so) instead of a regular executable file
- `-o libA3.so` -> tells the compiler to save the output to `libA3.so` file
- `fPIC` -> stands for Position-Independent Code. Needed for creating shared libraries.
- `-I"$JAVA_HOME/include"` and `-I"$JAVA_HOME/include/linux"` -> `-I` flag used for specifiying directories to include. Values in double quotes are directories
- `A3.c` -> name of the C program file to compile
- Lastly, run the program using `java -Djava.library.path=. A3`
- `java` -> Loads Java Virtual Machine (JVM)
- `-Djava.library.path=.` -> `-D` is used to set a system property. In this case, we’re setting the `java.library.path` (for .so or .dll files) property.
- `A3` -> name of the Java class containing the main method
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Codes/Group A/Assignment-A3/README.md
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### Refer [EXPLANATION](https://git.kska.io/sppu-te-comp-content/SystemsProgrammingAndOperatingSystem/src/branch/main/Codes/Group%20A/Assignment-A3/EXPLANATION.md) to understand how everything works.
> [!IMPORTANT]
> Tested on Linux and Windows.