C++ AST & Parsing

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.

Abstract Syntax Tree Explorer

AST Structure

TranslationUnit

FunctionDecl: fibonacci

BuiltinType: int

ParmVarDecl: n(int)

CompoundStmt

IfStmt

ReturnStmt

Source Code

int fibonacci(int n) { if (n <= 1) { return n; } return fibonacci(n - 1) + fibonacci(n - 2); }

🎯 Tip: Click on any node to see its source location highlighted. The AST represents the hierarchical structure of your code, with each node containing type information and relationships.

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

Enables optimization: Compilers analyze and transform the tree
Powers tooling: IDEs use AST for refactoring and analysis
Template processing: AST manipulation for template instantiation
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

Table of Contents

Abstract Syntax Tree Explorer

AST Structure

Source Code