From e112f896a215e79ea249a715f128c73c1da04e7a Mon Sep 17 00:00:00 2001
From: Fredrik Roubert <roubert@google.com>
Date: Thu, 30 Nov 2023 20:07:03 +0100
Subject: [PATCH] ICU-22576 Use standard alignof() with modern C.

---
 .ci-builds/.azure-pipelines.yml       | 6 +++---
 icu4c/source/test/cintltst/ccapitst.c | 9 ++++++---
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/.ci-builds/.azure-pipelines.yml b/.ci-builds/.azure-pipelines.yml
index c0599ad9f5ec..bb4b5fc8b7cf 100644
--- a/.ci-builds/.azure-pipelines.yml
+++ b/.ci-builds/.azure-pipelines.yml
@@ -164,7 +164,7 @@ jobs:
       displayName: 'Build only (WarningsAsErrors)'
       env:
         CC: clang-16
-        CPPFLAGS: '-Werror -Wno-strict-prototypes -Wno-gnu-offsetof-extensions -Wall -Wextra -Wextra-semi -Wundef -Wnon-virtual-dtor -Wsuggest-override'
+        CPPFLAGS: '-Werror -Wno-strict-prototypes -Wall -Wextra -Wextra-semi -Wundef -Wnon-virtual-dtor -Wsuggest-override'
         CXX: clang++-16
 #-------------------------------------------------------------------------
 - job: ICU4C_Clang16_Cpp20_Ubuntu_2004
@@ -188,7 +188,7 @@ jobs:
       displayName: 'Build and Test'
       env:
         CC: clang-16
-        CPPFLAGS: '-Werror -Wno-strict-prototypes -Wno-gnu-offsetof-extensions'
+        CPPFLAGS: '-Werror -Wno-strict-prototypes'
         CXX: clang++-16
         CXXFLAGS: '-std=c++20'
 #-------------------------------------------------------------------------
@@ -213,7 +213,7 @@ jobs:
       displayName: 'Build and Test'
       env:
         CC: clang-16
-        CPPFLAGS: '-Werror -Wno-strict-prototypes -Wno-gnu-offsetof-extensions'
+        CPPFLAGS: '-Werror -Wno-strict-prototypes'
         CXX: clang++-16
         CXXFLAGS: '-std=c++20 -stdlib=libc++'
 #-------------------------------------------------------------------------
diff --git a/icu4c/source/test/cintltst/ccapitst.c b/icu4c/source/test/cintltst/ccapitst.c
index 376388bf4f2c..48ad77c92f2b 100644
--- a/icu4c/source/test/cintltst/ccapitst.c
+++ b/icu4c/source/test/cintltst/ccapitst.c
@@ -37,8 +37,11 @@
 #define MAX_FILE_LEN 1024*20
 #define UCS_FILE_NAME_SIZE 512
 
-/* Similar to C++ alignof(type)  */
-#define ALIGNOF(type) offsetof (struct { char c; type member; }, member)
+#if __STDC_VERSION__ < 201112
+# define alignof(type) offsetof (struct { char c; type member; }, member)
+#elif __STDC_VERSION__ < 202311
+# include <stdalign.h>
+#endif
 
 /*returns an action other than the one provided*/
 #if !UCONFIG_NO_LEGACY_CONVERSION
@@ -1837,7 +1840,7 @@ static void TestConvertSafeClone()
             /* close the original immediately to make sure that the clone works by itself */
             ucnv_close(cnv);
 
-            if( actualSizes[idx] <= (bufferSizes[j] - (int32_t)ALIGNOF(UConverter)) &&
+            if( actualSizes[idx] <= (bufferSizes[j] - (int32_t)alignof(UConverter)) &&
                 err == U_SAFECLONE_ALLOCATED_WARNING
             ) {
                 log_err("ucnv_safeClone(%s) did a heap clone although the buffer was large enough\n", names[idx]);