From 680d5fe9ad91c73100cb0a581ec7a6f1c41b7b07 Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@tavianator.com>
Date: Mon, 7 Jul 2025 12:50:11 -0400
Subject: bfs.h: New container_of macro

---
 src/bfs.h | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

(limited to 'src')

diff --git a/src/bfs.h b/src/bfs.h
index 078feed..bb83df2 100644
--- a/src/bfs.h
+++ b/src/bfs.h
@@ -8,6 +8,9 @@
 #ifndef BFS_H
 #define BFS_H
 
+#include <assert.h> // For __GLIBC__
+#include <stddef.h> // For offsetof
+
 // Standard versions
 
 /** Possible __STDC_VERSION__ values. */
@@ -53,11 +56,18 @@ extern const char bfs_cflags[];
 extern const char bfs_ldflags[];
 extern const char bfs_ldlibs[];
 
-// Get __GLIBC__
-#include <assert.h>
-
 // Fundamental utilities
 
+/**
+ * Given `ptr = &t->member`, return `t`.
+ */
+#define container_of(ptr, type, member) \
+	(container_of_typecheck(ptr, type, member), \
+	 (type *)((char *)ptr - offsetof(type, member)))
+
+#define container_of_typecheck(ptr, type, field) \
+	(void)sizeof(ptr - &((type *)NULL)->field)
+
 /**
  * A preprocessor conditional.
  *
-- 
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