# CMake Executables and Libraries

**`add_executable(name source1.cpp source2.cpp)` builds an executable from source files. `add_library(name source1.cpp ...)` builds a library** — either static (.a, .lib) or shared (.so, .dll) depending on the type specified.

Building an executable:

```cmake
add_executable(myapp main.cpp)
add_executable(myapp main.cpp util.cpp helper.cpp)
```

The first creates an executable from one source file. The second lists multiple sources. You can also use glob patterns to find sources:

```cmake
file(GLOB SOURCES "src/*.cpp")
add_executable(myapp ${SOURCES})
```

Building libraries:

```cmake
add_library(mylib STATIC source.cpp)   # static library (.a or .lib)
add_library(mylib SHARED source.cpp)   # shared library (.so or .dll)
add_library(mylib source.cpp)          # default: STATIC on most systems
add_library(mylib INTERFACE)           # header-only: no compilation
```

Static libraries are linked into the final executable (no runtime dependency). Shared libraries are loaded at runtime (smaller executable, but library must be available).

Modern practice: use `target_sources()` instead of listing files in `add_executable()` or `add_library()`:

```cmake
add_executable(myapp)
target_sources(myapp PRIVATE main.cpp util.cpp)
```

This is clearer when building complex targets with conditional sources or generated files.

Specifying sources:

```cmake
add_executable(myapp
  src/main.cpp
  src/utils.cpp
  include/utils.h
)
```

Header files can be included (for IDE project generation and dependency tracking), but only `.cpp` files are actually compiled.

Use `add_library()` for anything reusable: core logic, utilities, third-party wrappers. Use `add_executable()` for entry points and tools. Both can link to other targets via `target_link_libraries()`.