Add a test for a global locale that changes the digit separator

Author: phlptp

tests/CMakeLists.txt

@@ -49,6 +49,7 @@ set(CLI11_TESTS
     StringParseTest
     ComplexTypeTest
     TrueFalseTest
+    localeTest
     OptionGroupTest
     EncodingTest)
 

tests/localeTest.cpp

@@ -0,0 +1,45 @@
+// Copyright (c) 2017-2025, University of Cincinnati, developed by Henry Schreiner
+// under NSF AWARD 1414736 and by the respective contributors.
+// All rights reserved.
+//
+// SPDX-License-Identifier: BSD-3-Clause
+
+#include "app_helper.hpp"
+
+#include <complex>
+#include <cstdint>
+#include <iomanip>
+#include <iostream>
+#include <locale>
+#include <numeric>
+#include <string>
+#include <utility>
+#include <vector>
+
+// Custom facet for thousands separator
+class CustomThousandsSeparator : public std::numpunct<char> {
+  protected:
+    char do_thousands_sep() const override { return '|'; }     // Space separator
+    std::string do_grouping() const override { return "\2"; }  // Group digits in sets of 2
+};
+
+// derived from https://github.com/CLIUtils/CLI11/pull/1160
+TEST_CASE_METHOD(TApp, "locale", "[separators]") {
+    std::locale customLocale(std::locale::classic(), new CustomThousandsSeparator);
+    std::locale::global(customLocale);  // Set as the default system-wide locale
+
+    // Ensure standard streams use the custom locale automatically
+    std::cout.imbue(std::locale());
+    std::int64_t foo;
+    std::uint64_t bar;
+    float qux;
+
+    app.add_option("FOO", foo, "Foo option")->default_val(1234567)->force_callback();
+    app.add_option("BAR", bar, "Bar option")->default_val(2345678)->force_callback();
+    app.add_option("QUX", qux, "QUX option")->default_val(3456.78)->force_callback();
+
+    CHECK_NOTHROW(run());
+    CHECK(foo == 1234567);
+    CHECK(bar == 2345678);
+    CHECK_THAT(qux, Catch::Matchers::WithinAbs(13456.78, 0.01));
+}

tests/meson.build

@@ -57,6 +57,7 @@ testnames = [
     ['StringParseTest', {}],
     ['ComplexTypeTest', {}],
     ['TrueFalseTest', {}],
+    ['localeTest', {}],
     ['OptionGroupTest', {}],
     ['EncodingTest', {}],
     # multi-only