C++ Linking Overview

How C++ object files are linked into executables. Learn symbol resolution, static vs dynamic linking, and linker optimization.

The Linking Process

Linking combines object files and libraries into a final executable, resolving symbols and fixing addresses.

What the Linker Does

Symbol Resolution
- Match undefined symbols with definitions
- Handle name mangling
- Resolve weak/strong symbols
Section Merging
- Combine .text sections (code)
- Merge .data sections (initialized data)
- Unite .bss sections (uninitialized data)
Relocation
- Adjust addresses to final locations
- Fix function calls and data references
- Update jump targets
Library Handling
- Include needed functions from libraries
- Static: Copy code into executable
- Dynamic: Create references for runtime

Types of Linking

Static Linking

# Create static library
ar rcs libstatic.a file1.o file2.o

# Link statically
g++ main.o libstatic.a -o program

Dynamic Linking

# Create shared library
g++ -shared -fPIC -o libshared.so file1.o file2.o

# Link dynamically
g++ main.o -L. -lshared -o program

Common Link Commands

# Basic linking
g++ main.o utils.o -o program

# With libraries
g++ main.o -lm -lpthread -o program

# Specify library path
g++ main.o -L/usr/local/lib -lmylib

# View symbols
nm program

# Check dependencies
ldd program

Link Order Matters

Libraries should come after the objects that use them:

# Wrong (may fail)
g++ -lmylib main.o

# Correct
g++ main.o -lmylib

# Circular dependencies
g++ main.o -lA -lB -lA

Linking Topics

Deep dive into specific aspects:

🔗 Symbol Resolution - How symbols are matched
📚 Dynamic Linking - Runtime library loading
🎯 Static vs Dynamic - Trade-offs and use cases

What's Next?

After linking creates the executable:

Program Loading - How the OS loads your program
Memory Layout - Runtime memory organization

Related concepts

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