From b3e9e62599532050fc776c5e8f076915b56c2235 Mon Sep 17 00:00:00 2001
From: David Faulkner <d@davo.co>
Date: Fri, 7 Aug 2026 23:40:47 -0500
Subject: Import official C23 code examples for Modern C (Jens Gustedt, 2024)

- Add official C source files, Makefile, c23-fallback.h, and LICENSE
- Update README.md with study mirror notice
---
 lifetime.c | 89 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 89 insertions(+)
 create mode 100644 lifetime.c

(limited to 'lifetime.c')

diff --git a/lifetime.c b/lifetime.c
new file mode 100644
index 0000000..ed12c10
--- /dev/null
+++ b/lifetime.c
@@ -0,0 +1,89 @@
+#include <stdio.h>
+#include "c23-fallback.h"
+
+void fgoto(unsigned n) {
+  unsigned j = 0;
+  unsigned* p = nullptr;
+  unsigned* q;
+ AGAIN:
+  if (p) printf("%u: p and q are %s, *p is %u\n",
+                j,
+                (q == p) ? "equal" : "unequal",
+                *p);
+  q = p;
+  p = &((unsigned){ j, }); /*@\label{lifetime_compound_literal}*/
+  ++j;
+  if (j <= n) goto AGAIN;
+}
+
+void fgotoblock(unsigned n) {
+  unsigned j = 0;
+  unsigned* p = nullptr;
+  unsigned* q;
+ AGAIN:  // Using a compound statement creates a new object at each iteration.
+  {      // A good modern compiler should complain that it is uninitialized.
+    if (p) printf("%u: p and q are %s, *p is %u\n",
+                  j,
+                  (q == p) ? "equal" : "unequal",
+                  *p);
+    q = p;
+    p = &((unsigned){ j, });
+    ++j;
+    if (j <= n) goto AGAIN;
+  }
+}
+
+__attribute__((noinline))
+void ffor1(void) {
+  unsigned j = 1;
+  printf("%u: p and q are %s, *p is %u\n",
+         j,
+         "unequal",
+         j-1);
+}
+
+__attribute__((noinline))
+void fforn(unsigned n) {
+  ffor1();
+  for (unsigned j = 2; j <= n; ++j) {
+    printf("%u: p and q are %s, *p is %u\n",
+           j,
+           "equal",
+           j-1);
+  }
+}
+
+void ffor(unsigned n) {
+  switch (n) {
+  case 0: break;
+  case 1: ffor1(); break;
+  default: fforn(n); break;
+  }
+}
+
+void fVLA(unsigned n) {
+  unsigned volatile j = 0;
+  unsigned* p = nullptr;
+  unsigned* q;
+ AGAIN:
+  {
+    if (p) printf("%u: p and q are %s\n",
+                  j,
+                  (q == p) ? "equal" : "unequal");
+    q = p;
+    unsigned VLA[j+1];
+    for (unsigned i = 0; i <= j; ++i)
+      VLA[i] = j;
+    p = VLA;
+    ++j;
+    if (j <= n) goto AGAIN;
+  }
+}
+
+
+
+int main(int argc, [[maybe_unused]] char* argv[]) {
+  fgoto(argc+1);
+  fgotoblock(argc+1);
+  ffor(argc+1);
+}
-- 
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