add build post

Author: sonjh1217

_posts/2025-09-23-Build-Librarymd.md

@@ -0,0 +1,33 @@
+---
+title:  "How iOS Apps Are Built: From Source Code to Libraries"
+
+categories:
+  - iOS
+  - Basic Concept
+tags:
+  - Library
+  - Build
+---
+
+![image](./assets/img/post/build.png)
+
+## Static Library vs. Dynamic Library
+1. How to include in an app
+    1. Static libraries: You only need to **Link**.
+    1. Dynamic libraries: You need to **Link + Embed**.
+        1. Link writes Dynamic Library References (LC_LOAD_DYLIB) into the executable.
+        1. Embed places the linked library binary (the .dylib inside the .framework) into the app bundle (usually at .app/Frameworks) and signs it.
+    1. The settings for linking and embedding (e.g., Link Binary With Libraries) are often managed automatically by dependency managers such as SPM, CocoaPods, or Carthage.
+1. Advantages
+    1. Static libraries
+        1. Faster launch time
+        1. Dead-code strip
+    1. Dynamic libraries
+        1. Shared across targets or modules
+        1. Faster linking, since all `.o` files do not need to be merged into the executable
+        1. With ABI stability (Library Evolution enabled), incremental rebuilds can often be avoided when the library changes
+        
+## System Framework (ex. UIKit, Foundation)
+They are provided as dynamic libraries, but they are **embedded in the OS**. Therefore, you only need to link. Basic frameworks such as UIKit and Foundation are linked when you make an app template. But for additional frameworks such as ARKit, you need to link.        
+
+