Difference between Binary Compatibility and Source Compatibility in C++

In this article, we will discuss the differences between Binary Compatibility and Source Compatibility in C++. Before discussing their differences, we must know about Binary Compatibility and Source Compatibility in C++ with their examples.

What is the Binary Compatibility?

Binary compatibility in C++ refers to the fact that a built binary (executable or library) does not require recompilation when linked with various versions of other binaries. It is necessary so that libraries or APIs can be updated without requiring the rewriting of dependent programs. It ensures that the memory order, function headings, and the size of classes are structured in a compatible way. Any modifications to class definitions, virtual tables, and function definitions may violate binary compatibility as some dependencies between programs are considered broken whenever there are any significant changes, especially during program execution, even when the original source code remains the same.

• Importance: It must be done when distributing precompiled libraries and common objects. Users should not need to recompile their apps in order to update the library.
• Example: When a library modifies its internal implementation without changing the public interface (function signatures, class sizes, memory layout, etc.), programs that already use it can keep running without needing to be recompiled.
• Breaking Mutual Compatibility in Binary: Changing the size of a class, a method's signature, the body of the data structure, and even the physical layout of a virtual table might lead to loss of binary compatibility.

What is the Source Compatibility?

When the C++ source code can compile without changes due to the code itself, it is said to be upwardly compatible with new libraries or compilers. If the public interfaces of the API do not change (say, function signatures and classes), source code can be recompiled using new libraries. When an alteration is made to an API that breaks old code so that it has no longer compiles against the new library version, and then it is breaking source compatibility. Examples are adding, removing, or modifying functions or templates.

• Importance: Where there has been an upgrade of the libraries or compilers, changes may be made to the source code of the application, which would affect the library without any adverse effects on issues related to compilation.
• For example, if a library function changes its implementation while keeping the same interface (declaration, parameters, and return types) so that applications written for older library versions can compile against the new version without any modifications, breaking source compatibility has occurred.

Key differences between Binary Compatibility and Source Compatibility in C++:

• Binary compatibility focusses on the ability to run the same compiled code (binaries) with updated components, whereas source compatibility ensures that source code can still be created with different versions of dependencies.
• Breaking binary compatibility may not affect source compatibility and vice versa. We may change internal data structures without impacting the public interface; it would harm binary compatibility while maintaining source compatibility.

Head-to-head comparison between Binary Compatibility and Source Compatibility in C++:

There are several main differences between Binary Compatibility and Source Compatibility in C++. Some main differences are as follows:

Conclusion:

In conclusion, Source and binary code compatibility are of good significance in the design of C++ software with special reference to dynamic codebases, libraries, and APIs. This is where the source and binary incompatibilities would cause runtime problems or crash while trying to install an update or make an upgrade. The ability of different copies of the libraries and programs working with each other to not cause any runtime issues and allow updates to flow smoothly is known as binary compatibility. When an updated version, recompiled against modifications and enhancements made to the library or API, can be generated using the same source code base, the developers are less likely to break any functionality regarding refactoring dependencies, and software systems must be reliable, easily upgradeable, and maintainable.