Understanding Static Linking with Conan
When working with C++ projects, Conan is a powerful package manager that automates dependency management, but how it handles static linking can feel a bit magical. Let’s break it down and demystify the process.
What Happens During conan install?
When you run conan install, Conan:
- Resolves dependencies listed in your
conanfile.pyorconanfile.txt. - Downloads prebuilt binaries from remotes (like ConanCenter) if they match your profile.
- Builds from source if necessary and stores the result in the local Conan cache.
- Generates build info and configuration files (like
conan_toolchain.cmake).
How Does Static Linking Work?
Static linking means combining your code with the library code at compile time. If a Conan package is built as a static library, it produces a .a file (on Unix-like systems) or .lib file (on Windows). This file:
- Contains compiled object files (.o files)
- Is not executable (no
main()) - Is linked into your final
.exeduring compilation
Once linked, the contents of the .a file are baked into your final executable — which is why you don’t need the static library present at runtime.
Static vs Shared Summary
| File Type | Built by Conan? | Needed at Runtime? | Contains main()? |
Use Case |
|---|---|---|---|---|
.a |
✅ | ❌ | ❌ | Linked into final executable |
.so/.dll |
✅ | ✅ | ❌ | Dynamically loaded at runtime |
.exe |
❌ (your code builds it) | ✅ | ✅ | Final application binary |
Why Macro Consistency Matters
Static libraries are compiled with a specific set of macros and flags. If your application code includes headers from the static library but uses a different set of macros, things can go wrong.
For example:
// header
#ifdef USE_COOL_FEATURE
void cool_feature();
#else
void fallback_feature();
#endif
If the library was built with USE_COOL_FEATURE defined, but your code doesn't define it, the linker will look for fallback_feature() — which doesn’t exist in the static lib. This causes linker errors or worse: subtle runtime bugs.
Best Practices to Avoid Macro Mismatches
- Use the same macro definitions as the library was built with.
- Let Conan manage flags and definitions using
conan_toolchain.cmake. - Inspect Conan package options using
conan inspect <package-ref>. - If you use your own build scripts, make sure to apply the generated macros manually.
Proper understanding of static linking and build configuration is essential to avoid hard-to-debug issues. With Conan, most of this can be automated — as long as your macros and profiles are consistent.