Part: Eliminate use of sscanf

Replace with safer modern C++ `std::from_chars` (plus some additional
validation for expected inputs). Includes unit tests for new function.

src/App/ElementNamingUtils.cpp

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: LGPL-2.1-or-later
 
 #include "ElementNamingUtils.h"
+#include <charconv>
 #include <boost/algorithm/string/predicate.hpp>
 
 
@@ -123,3 +124,20 @@ const std::string Data::indexSuffix(int index, const char* label)
     name += std::to_string(index);
     return name;
 }
+
+int Data::indexOfElement(std::string_view s, std::string_view prefix)
+{
+    int idx = 0;
+    if (prefix.empty()) {
+        return idx;
+    }
+    if (s.starts_with(prefix)) {
+        auto num = s.substr(prefix.size());
+        auto [ptr, ec] = std::from_chars(num.data(), num.data() + num.size(), idx);
+
+        if (ec != std::errc{} || ptr != num.data() + num.size()) {
+            return 0;
+        }
+    }
+    return idx;
+}

src/App/ElementNamingUtils.h

@@ -3,6 +3,7 @@
 #pragma once
 
 #include <string>
+#include <string_view>
 #include <utility>
 #include "FCGlobal.h"
 
@@ -119,5 +120,8 @@ AppExport const char *hasMappedElementName(const char *subname);
 
 AppExport const std::string indexSuffix(int index, const char *label=ELEMENT_MAP_INDEX);
 
+/// Given a string and a prefix, return the integer index that follows that prefix, or 0 if not found
+AppExport int indexOfElement(std::string_view s, std::string_view prefix);
+
 }  // namespace Data
 // clang-format on

src/Mod/Part/App/PartFeature.cpp

@@ -1987,9 +1987,8 @@ void FilletBase::onUpdateElementReference(const App::Property* prop)
             FC_WARN("fillet edge count mismatch in object " << getFullName());
             break;
         }
-        int idx = 0;
-        sscanf(subs[i].c_str(), "Edge%d", &idx);
-        if (idx) {
+        int idx = Data::indexOfElement(subs[i], "Edge");
+        if (idx != 0) {
             values[i].edgeid = idx;
         }
         else {

src/Mod/Part/Gui/DlgFilletEdges.cpp

@@ -48,6 +48,7 @@
 #include <App/Application.h>
 #include <App/Document.h>
 #include <App/DocumentObject.h>
+#include <App/ElementNamingUtils.h>
 #include <Base/UnitsApi.h>
 #include <Base/Tools.h>
 #include <Gui/Application.h>
@@ -674,8 +675,7 @@ void DlgFilletEdges::setupFillet(const std::vector<App::DocumentObject*>& objs)
         for (size_t i = 0; i < e.size(); ++i) {
             auto& sub = subs[i];
             if (sub.newName.empty()) {
-                int idx = 0;
-                sscanf(sub.oldName.c_str(), "Edge%d", &idx);
+                int idx = Data::indexOfElement(sub.oldName, "Edge");
                 if (idx == 0) {
                     FC_WARN("missing element reference: " << sub.oldName);
                 }

tests/src/App/ElementNamingUtils.cpp

@@ -59,4 +59,29 @@ TEST_F(ElementNamingUtilsTest, findElementName)
     EXPECT_STREQ(name3, "Edge3");
     EXPECT_STREQ(name4, "Edge4");
 }
+
+TEST_F(ElementNamingUtilsTest, indexOfElement)
+{
+    // Valid cases
+    EXPECT_EQ(Data::indexOfElement("Edge1", "Edge"), 1);
+    EXPECT_EQ(Data::indexOfElement("Edge12", "Edge"), 12);
+    EXPECT_EQ(Data::indexOfElement("Edge999", "Edge"), 999);
+
+    // Prefix mismatch
+    EXPECT_EQ(Data::indexOfElement("Node5", "Edge"), 0);
+
+    // Missing numeric suffix
+    EXPECT_EQ(Data::indexOfElement("Edge", "Edge"), 0);
+
+    // Non-numeric suffix
+    EXPECT_EQ(Data::indexOfElement("EdgeX", "Edge"), 0);
+    EXPECT_EQ(Data::indexOfElement("Edge12X", "Edge"), 0);
+
+    // Zero or invalid index
+    EXPECT_EQ(Data::indexOfElement("Edge0", "Edge"), 0);
+
+    // Degenerate inputs
+    EXPECT_EQ(Data::indexOfElement("", "Edge"), 0);
+    EXPECT_EQ(Data::indexOfElement("123", ""), 0);
+}
 // NOLINTEND(readability-magic-numbers)