From c7a27167e2dfcdf62d6c4d096bbbe68a758e7e24 Mon Sep 17 00:00:00 2001
From: Danilo Piparo <danilo.piparo@cern.ch>
Date: Fri, 20 Dec 2024 14:14:11 +0100
Subject: [PATCH] [math] Support locales for which the decimal separator is ,

fixes #17225
---
 hist/hist/src/TFormula.cxx       |  4 +++-
 hist/hist/test/test_TFormula.cxx | 25 ++++++++++++++++++++++++-
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/hist/hist/src/TFormula.cxx b/hist/hist/src/TFormula.cxx
index 972aed876a9e2..ba0e2cc1ee5b1 100644
--- a/hist/hist/src/TFormula.cxx
+++ b/hist/hist/src/TFormula.cxx
@@ -2263,7 +2263,9 @@ void TFormula::ProcessFormula(TString &formula)
          map<TString, Double_t>::iterator constIt = fConsts.find(fun.GetName());
          if (constIt != fConsts.end()) {
             TString pattern = TString::Format("{%s}", fun.GetName());
-            TString value = TString::Format("%lf", (*constIt).second);
+            // #17225: we take into account LC_LOCALE settings for which the decimal separator
+            // is , instead of ., e.g. de_AT.UTF-8
+            TString value = TString::Format("%lf", (*constIt).second).ReplaceAll(",", ".");
             formula.ReplaceAll(pattern, value);
             fun.fFound = true;
             // std::cout << "constant with name " << fun.GetName() << " is found " << std::endl;
diff --git a/hist/hist/test/test_TFormula.cxx b/hist/hist/test/test_TFormula.cxx
index ca284cee33c21..834505abf447e 100644
--- a/hist/hist/test/test_TFormula.cxx
+++ b/hist/hist/test/test_TFormula.cxx
@@ -2,8 +2,31 @@
 
 #include "TFormula.h"
 
+#include <locale.h>
+
+#ifdef R__HAS_GEOM
 // Test that autoloading works (ROOT-9840)
 TEST(TFormula, Interp)
 {
-  TFormula f("func", "TGeoBBox::DeclFileLine()");
+   TFormula f("func", "TGeoBBox::DeclFileLine()");
+}
+#endif
+
+class localeRAII {
+   std::string fLocale;
+
+public:
+   localeRAII() : fLocale(setlocale(LC_NUMERIC, nullptr)){};
+   ~localeRAII() { setlocale(LC_NUMERIC, fLocale.c_str()); }
+};
+
+// #17225
+TEST(TFormula, Locale)
+{
+   localeRAII lraii;
+   setlocale(LC_NUMERIC, "de_AT.UTF-8");
+   TFormula f0("f0", "gausn(x)");
+   EXPECT_TRUE(f0.IsValid());
+   TFormula f1("f1", "landau(x)");
+   EXPECT_TRUE(f1.IsValid());
 }