- Compiling transforms source code into executable machine code.
- A compiler performs lexical, syntactic and semantic analysis.
- There are AOT, JIT, cross compilers and transpilers.
- Compiled code is faster than interpreted code.
If you've ventured into the world of programming, you've probably heard the term " compile ." This concept is fundamental to software development, as it defines the process by which source code written in a programming language is transformed into a format that a computer can executable.
Understanding what compiling means and how a compiler works is essential for any programmer who wants to optimize their code and better understand how programming languages work. Below, we explain in detail what this process entails, the types of compilers that exist, and the key differences between compiled and interpreted code.
What is compiling?
Compiling is the process of translating source code from a high-level language (such as C++, Java, or Rust) into binary code or machine code, which the computer's processor can directly execute.
Source code is written in a language that humans can read and understand, but computers can only interpret binary code. Therefore, a specific program called a compiler is required to convert the source code into executable code. If you would like to learn more about this topic, you can consult our guide on the concepts and differences between compilers and interpreters.
What is a compiler and how does it work?
A compiler is a program specialized in transforming source code into object code or executable code. This conversion process consists of several phases:
1. Preprocessing
Before compilation, the source code goes through a preprocessing phase where macros are expanded, necessary files are included, and other modifications are made before generating the code that is actually compiled.
2. Lexical analysis
The compiler scans the source code and divides it into tokens , which are the smallest units of meaning in the programming language, such as keywords, identifiers, and operators.
3. Syntactic analysis
In this phase, the code structure is checked to ensure it is correct according to the grammar of the programming language. If there are syntax errors, the compiler will detect them and tell the programmer where they are so they can be corrected.
4. Semantic analysis
The compiler checks that the operations and expressions in the code make logical sense. It verifies that variables and functions are well-defined and that valid operations are performed. This is crucial to ensure your code compiles without problems.
5. Intermediate code generation
After verifying the syntax and semantics of the code, the compiler generates intermediate code , a simplified representation that can be optimized before the final translation to machine code.
6. Code optimization
At this stage, the compiler improves the generated code to make it more efficient and reduce memory consumption and processing time.
7. Machine code generation
Finally, the intermediate code is converted into machine code instructions specific to the computer's processor architecture. This part of the process is vital to ensure that the program will function correctly on the hardware.
8. Linking
The generated object code is combined with libraries and other modules required to produce the final executable file. How these libraries are managed is interesting, and for this, a specialized compiler can be useful, such as those you can find in our section on compilers for the C language.
Types of compilers
There are different types of compilers depending on their operation and purpose:
- AOT (Ahead-Of-Time) Compilers: They compile all the code before executing it. Examples: GCC, Clang.
- JIT (Just-In-Time) compilers: They compile the code during execution to improve performance. Examples: JVM for Java, V8 for JavaScript. For a deeper understanding of this type, we suggest you our guide on Just-In-Time compilers.
- Cross compilers: They generate executable code for a platform other than the one they are running on. If you are interested, you can read about Cross compilers in detail.
- Transpilers: They transform code from one high-level language to another, such as TypeScript to JavaScript.
Compiled code vs interpreted code
One of the main differences in program execution is whether the code is compiled or interpreted :
- Compiled code: It is fully translated before running and is usually faster. Example: C, C++.
- Interpreted code: Translated line by line at runtime, facilitating portability but reducing performance. Example: Python, JavaScript.
Practical compilation example
Suppose you write a program in C:
#include int main() { printf("Hello, world!\n"); return 0; }
To compile this code with GCC in a terminal, you would run:
gcc program.c -o program
Throughout the article we have explored the compilation process in depth, from its definition to its importance in software development. While interpreted languages offer flexibility, compiled languages stand out for their efficiency. Understanding how a compiler works and the phases of the process is key to improving our skills as programmers.
