From 7cff6d14ef59d3faa70a0c36a5f75a490a66f2a1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Marjam=C3=A4ki?= <daniel.marjamaki@cppcheck.com>
Date: Sat, 7 Nov 2026 11:57:29 +0100
Subject: [PATCH] Fix #726 (#if: ?: treats a zero condition as true unless it
 is written exactly as 0)

?: and ! compared the operand with the string "0", so zero values such as
00, -0 and 0L were taken as true. Compare the numeric value instead.
---
 simplecpp.cpp |  4 ++--
 test.cpp      | 27 +++++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/simplecpp.cpp b/simplecpp.cpp
index 91af52ea..60f879cc 100644
--- a/simplecpp.cpp
+++ b/simplecpp.cpp
@@ -1305,7 +1305,7 @@ void simplecpp::TokenList::constFoldUnaryNotPosNeg(simplecpp::Token *tok)
             tok->setstr(tok->next->str());
             deleteToken(tok->next);
         } else if (tok->op == '!' && tok->next && tok->next->number) {
-            tok->setstr(tok->next->str() == "0" ? "1" : "0");
+            tok->setstr(stringToLL(tok->next->str()) == 0 ? "1" : "0");
             deleteToken(tok->next);
         } else if (tok->op == '~' && tok->next && tok->next->number) {
             tok->setstr(toString(~stringToLL(tok->next->str())));
@@ -1571,7 +1571,7 @@ void simplecpp::TokenList::constFoldQuestionOp(Token *&tok1)
             deleteToken(trueTok);
             deleteToken(falseTok);
         } else {
-            Token * const result = (condTok->str() != "0" ? trueTok : falseTok);
+            Token * const result = (stringToLL(condTok->str()) != 0 ? trueTok : falseTok);
             if (condTok == tok1)
                 tok1 = result;
             deleteToken(condTok->next); // ?
diff --git a/test.cpp b/test.cpp
index bd0da227..1296c790 100644
--- a/test.cpp
+++ b/test.cpp
@@ -2887,6 +2887,32 @@ static void ifShortCircuit()
     ASSERT_EQUALS("file0,1,syntax_error,failed to evaluate #if condition, division/modulo by zero\n", toString(outputList));
 }
 
+static void ifZeroCondition()
+{
+    // a zero value that is not written as 0 is false
+    const char * const exprs[] = {
+        "00 ? 1 : 0",
+        "-0 ? 1 : 0",
+        "-X ? 1 : 0",
+        "0L ? 1 : 0",
+        "!00 ? 0 : 1",
+        "!0L ? 0 : 1"
+    };
+    for (const char * const expr : exprs) {
+        const std::string code = std::string("#if ") + expr + "\n"
+                                 "1\n"
+                                 "#else\n"
+                                 "2\n"
+                                 "#endif\n";
+        ASSERT_EQUALS("\n\n\n2", preprocess(code.c_str()));
+    }
+
+    // the selected operand is evaluated
+    simplecpp::OutputList outputList;
+    ASSERT_EQUALS("", preprocess("#if 00 ? 1 : 1/0\n#endif\n", &outputList));
+    ASSERT_EQUALS("file0,1,syntax_error,failed to evaluate #if condition, division/modulo by zero\n", toString(outputList));
+}
+
 static void ifTrueFalse()
 {
     const char code[] = "#if true && !false\n"
@@ -5123,6 +5149,7 @@ static void runTests(int argc, char **argv, Input input)
     TEST_CASE(ifoverflow);
     TEST_CASE(ifdiv0);
     TEST_CASE(ifShortCircuit);
+    TEST_CASE(ifZeroCondition);
     TEST_CASE(ifTrueFalse);
     TEST_CASE(ifalt); // using "and", "or", etc
     TEST_CASE(ifexpr);