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
---
 va_arg.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)
 create mode 100644 va_arg.c

(limited to 'va_arg.c')

diff --git a/va_arg.c b/va_arg.c
new file mode 100644
index 0000000..1b2c0a8
--- /dev/null
+++ b/va_arg.c
@@ -0,0 +1,52 @@
+#include "c23-fallback.h"
+#include <stdarg.h>
+#include <stdio.h>
+//#include <stdlib.h>
+
+/**
+ ** @brief A small, useless function to show how variadic
+ ** functions work
+ **/
+double sumIt(size_t n, ...) {
+  double ret = 0.0;
+  va_list va;
+  va_start(va);
+  for (size_t i = 0; i < n; ++i)
+    ret += va_arg(va, double);
+  va_end(va);
+  return ret;
+}
+
+/**
+ ** @brief A simple debug stream
+ **
+ ** Per convention no output is produced when this is null.
+ **
+ ** This can be set local to the current thread, such that threads may
+ ** print their debug messages to different files or streams.
+ **/
+thread_local FILE* iodebug = nullptr;
+
+/**
+ ** @brief Prints to the debug stream @c iodebug
+ **/
+[[gnu::format(printf, 1, 2)]]
+int printf_debug(const char *format, ...) {
+  int ret = 0;
+  if (iodebug) {
+    va_list va;
+    va_start(va);
+    ret = vfprintf(iodebug, format, va);
+    va_end(va);
+  }
+  return ret;
+}
+
+
+
+int main(int argc, char* argv[argc+1]) {
+  if (argc < 4) return EXIT_FAILURE;
+  iodebug = stderr;
+  printf_debug("%g\n", sumIt(3, strtod(argv[1], nullptr), strtod(argv[2], nullptr), strtod(argv[3], nullptr)));
+  return EXIT_SUCCESS;
+}
-- 
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