C++ AST & Parsing Explained

Abstract Syntax Tree (AST)

The AST is a tree representation of your code's syntactic structure. Each node represents a construct in the source code, from functions to expressions.

Parsing Phases

1. Lexical Analysis (Tokenization)

Breaks code into tokens:

• Keywords: int, if, return
• Identifiers: variable and function names
• Literals: 42, "string", 3.14
• Operators: +, ->, ::

2. Syntax Analysis

Builds the AST according to grammar rules:

function_declaration
├── return_type
├── function_name
├── parameter_list
└── compound_statement
    └── statements...

3. Semantic Analysis

• Type checking
• Name resolution
• Template instantiation
• Overload resolution

Why AST Matters

1. Enables optimization: Compilers analyze and transform the tree
2. Powers tooling: IDEs use AST for refactoring and analysis
3. Template processing: AST manipulation for template instantiation
4. Error detection: Semantic errors found through tree analysis

Viewing the AST

# Clang AST dump
clang++ -Xclang -ast-dump main.cpp

# GCC tree dump
g++ -fdump-tree-original main.cpp

Common AST Nodes

• FunctionDecl: Function declarations
• CompoundStmt: Block statements {...}
• IfStmt: Conditional statements
• CallExpr: Function calls
• BinaryOperator: Binary operations (+, -, *, /)
• DeclRefExpr: Variable references

Next Steps

• Learn about Compiler Optimization
• Understand Symbol Tables
• Explore the Preprocessor

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