From ee3966f762eb7d4cea0e4cff78ad90be81f36b01 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ludvig=20Gunne=20Lindstr=C3=B6m?=
 <ludviggunnelindstrom@gmail.com>
Date: Thu, 3 Jul 2025 12:12:03 +0200
Subject: [PATCH 1/2] add tests

---
 test.cpp | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/test.cpp b/test.cpp
index 45498a08..6070c9e0 100644
--- a/test.cpp
+++ b/test.cpp
@@ -1617,6 +1617,48 @@ static void has_include_6()
     ASSERT_EQUALS("", preprocess(code));
 }
 
+static void strict_ansi_1()
+{
+    const char code[] = "#if __STRICT_ANSI__\n"
+                        " A\n"
+                        "#endif";
+    simplecpp::DUI dui;
+    dui.std = "gnu99";
+    ASSERT_EQUALS("", preprocess(code, dui));
+}
+
+static void strict_ansi_2()
+{
+    const char code[] = "#if __STRICT_ANSI__\n"
+                        " A\n"
+                        "#endif";
+    simplecpp::DUI dui;
+    dui.std = "c99";
+    ASSERT_EQUALS("\nA", preprocess(code, dui));
+}
+
+static void strict_ansi_3()
+{
+    const char code[] = "#if __STRICT_ANSI__\n"
+                        " A\n"
+                        "#endif";
+    simplecpp::DUI dui;
+    dui.std = "c99";
+    dui.undefined.insert("__STRICT_ANSI__");
+    ASSERT_EQUALS("", preprocess(code, dui));
+}
+
+static void strict_ansi_4()
+{
+    const char code[] = "#if __STRICT_ANSI__\n"
+                        " A\n"
+                        "#endif";
+    simplecpp::DUI dui;
+    dui.std = "gnu99";
+    dui.defines.push_back("__STRICT_ANSI__");
+    ASSERT_EQUALS("\nA", preprocess(code, dui));
+}
+
 static void ifdef1()
 {
     const char code[] = "#ifdef A\n"
@@ -3181,6 +3223,11 @@ int main(int argc, char **argv)
     TEST_CASE(has_include_5);
     TEST_CASE(has_include_6);
 
+    TEST_CASE(strict_ansi_1);
+    TEST_CASE(strict_ansi_2);
+    TEST_CASE(strict_ansi_3);
+    TEST_CASE(strict_ansi_4);
+
     TEST_CASE(ifdef1);
     TEST_CASE(ifdef2);
     TEST_CASE(ifndef);

From 7dde25f3110e95c8684b58fc678506a44e8507e1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ludvig=20Gunne=20Lindstr=C3=B6m?=
 <ludviggunnelindstrom@gmail.com>
Date: Thu, 3 Jul 2025 12:01:48 +0200
Subject: [PATCH 2/2] fix #459

---
 simplecpp.cpp | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/simplecpp.cpp b/simplecpp.cpp
index d925773e..bccb9b1b 100755
--- a/simplecpp.cpp
+++ b/simplecpp.cpp
@@ -3480,11 +3480,14 @@ void simplecpp::preprocess(simplecpp::TokenList &output, const simplecpp::TokenL
 
     const bool hasInclude = isCpp17OrLater(dui) || isGnu(dui);
     MacroMap macros;
+    bool strictAnsiDefined = false;
     for (std::list<std::string>::const_iterator it = dui.defines.begin(); it != dui.defines.end(); ++it) {
         const std::string &macrostr = *it;
         const std::string::size_type eq = macrostr.find('=');
         const std::string::size_type par = macrostr.find('(');
         const std::string macroname = macrostr.substr(0, std::min(eq,par));
+        if (macroname == "__STRICT_ANSI__")
+            strictAnsiDefined = true;
         if (dui.undefined.find(macroname) != dui.undefined.end())
             continue;
         const std::string lhs(macrostr.substr(0,eq));
@@ -3493,6 +3496,10 @@ void simplecpp::preprocess(simplecpp::TokenList &output, const simplecpp::TokenL
         macros.insert(std::pair<TokenString,Macro>(macro.name(), macro));
     }
 
+    const bool strictAnsiUndefined = dui.undefined.find("__STRICT_ANSI__") != dui.undefined.cend();
+    if (!isGnu(dui) && !strictAnsiDefined && !strictAnsiUndefined)
+        macros.insert(std::pair<TokenString, Macro>("__STRICT_ANSI__", Macro("__STRICT_ANSI__", "1", dummy)));
+
     macros.insert(std::make_pair("__FILE__", Macro("__FILE__", "__FILE__", dummy)));
     macros.insert(std::make_pair("__LINE__", Macro("__LINE__", "__LINE__", dummy)));
     macros.insert(std::make_pair("__COUNTER__", Macro("__COUNTER__", "__COUNTER__", dummy)));