Chapter 1: Introduction to C++ Compilation

In this guide, I aim to elucidate the intricate compilation process of a C++ program. We'll examine each phase, from the initial source code to the final optimized object code.

As a programmer, I frequently depend on compilers to convert high-level C++ code into a format that computers can efficiently interpret and execute. Yet, this seemingly straightforward task involves a series of complex steps that lead to the creation of the final executable.

• Preprocessing
• Compilation
• Assembly
• Linking

While I won't delve into the behind-the-scenes operations, I will outline the compilation levels of C++ code within a terminal environment. We will analyze the preprocessing phase, which includes expanding macros and incorporating header files. Following this, we will discuss the compilation phase, where the source code is translated into assembly or machine code. Next, we will explore the assembly stage, where human-readable assembly code is converted into binary object code, and finally, we will look into the linking stage, where various object files come together to form the final executable.

Compiling C++ code generally involves several stages, which can be categorized as follows:

Preprocessing

The preprocessor manages directives like #include, #define, and #ifdef. It expands macros and includes necessary header files. You can execute the preprocessor independently with the -E option in GCC: g++ -E source.cpp -o output.i.

Compilation

In this phase, the preprocessed source code is converted into assembly code (or directly into machine code in certain cases). The compiler checks for syntax and semantic errors, produces an intermediate representation, and optimizes the code. You can compile the source into assembly using the -S option: g++ -S source.cpp -o output.s.

Assembly

Assembly code is low-level and human-readable, tailored to the target architecture. The assembler converts this assembly code into machine code (object code). To assemble the code, use the -c option: g++ -c source.s -o source.o.

Linking

This stage merges object files (produced during compilation) along with libraries to create a single executable file. The linker resolves external references, integrates code sections, and generates the final executable. You can link object files into an executable using the compiler without any specific option: g++ source1.o source2.o -o executable.

All these stages can be executed with the correct options in a single command. For instance, to compile and link in one step, you would run: g++ source.cpp -o executable.

Here's a simplified example:

# Step 1: Preprocessing

g++ -E source.cpp -o source.i

# Step 2: Compilation

g++ -S source.i -o source.s

# Step 3: Assembly

g++ -c source.s -o source.o

# Step 4: Linking

g++ source.o -o executable

Alternatively, you can combine all steps into a single command:

g++ source.cpp -o executable

#### Example Code

Consider the following C++ code, which defines an array of integers and a function arraySum() that computes the sum of all elements in the array. The main() function initializes the array, calls arraySum() to calculate the sum, and displays the result. This code is saved in a file named source.cpp.

#include <iostream>

// Function to calculate the sum of elements in an array

int arraySum(int arr[], int size) {

int sum = 0;

for (int i = 0; i < size; ++i) {

sum += arr[i];

}

return sum;

}

int main() {

const int SIZE = 5;

int arr[SIZE] = {1, 2, 3, 4, 5};

// Calculate sum of array elements

int sum = arraySum(arr, SIZE);

// Display the result

std::cout << "Sum of array elements: " << sum << std::endl;

return 0;

}

Step 1: Preprocessing

After running g++ -E source.cpp -o source.i, the generated source.i file contains 32,277 lines. These lines comprise details about the source file, built-in files, included header files, and compiler directives encountered during preprocessing, aiding in code tracking and comprehension.

Step 2: Compilation

Executing g++ -S source.i -o source.s results in a source.s file with 172 lines of assembly code derived from the original C++ source code. Each assembly instruction corresponds to one or more machine instructions that perform equivalent operations.

Step 3: Assembly

This stage is crucial for those interested in compiler design and optimization. After g++ -c source.s -o source.o, the content of the source.s file cannot be opened directly using a text editor. Instead, you would use objdump -d source.o to review the object file contents. objdump provides information about object files, including disassembled machine code and symbol tables.

To disassemble the machine code/object file and view its contents, use objdump with the -d option. You can also display the symbol table and headers as needed.

Step 4: Linking

Upon executing g++ source.o -o executable, you now have the executable file. Running it should yield the expected result, which, in this case, would be:

./executable

This should output: Sum of array elements: 15.

Chapter 2: Video Resources

This video titled "Programming in the C language - [#3] Makefiles and Compiling" provides insights into the practical aspects of compiling code in C, which can serve as a foundation for understanding similar processes in C++.

In this tutorial, "Understanding the C Compilation Process | Step-by-Step Tutorial," you will find a detailed walkthrough of the steps involved in the C compilation process, further enhancing your knowledge on the topic.