Add APPEND mode to exodusIIcpp

.claude/settings.local.json

@@ -0,0 +1,8 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(head:*)",
+      "Bash(tail:*)"
+    ]
+  }
+}

include/exodusIIcpp/enums.h

@@ -8,7 +8,8 @@ namespace exodusIIcpp {
 /* clang-format off */
 enum class FileAccess {
     READ,
-    WRITE
+    WRITE,
+    APPEND
 };
 /* clang-format on */
 

include/exodusIIcpp/file.h

@@ -66,7 +66,8 @@ class File {
     /// @param file_path Path to the file to open/create
     /// @param file_access Desired file access
     ///  - ``exodusIIcpp::FileAccess::READ`` for reading,
-    ///  - ``exodusIIcpp::FileAccess::WRITE`` for writing.
+    ///  - ``exodusIIcpp::FileAccess::WRITE`` for writing,
+    ///  - ``exodusIIcpp::FileAccess::APPEND`` for appending to an existing file.
     explicit File(exodusIIcpp::fs::path file_path, exodusIIcpp::FileAccess file_access);
     ~File();
 
@@ -80,6 +81,11 @@ class File {
     /// @param file_path Path to the file to create
     void create(const std::string & file_path);
 
+    /// Open an existing ExodusII file for appending new time steps
+    ///
+    /// @param file_path Path to the file to open
+    void append(const std::string & file_path);
+
     /// Is file opened
     ///
     /// @return `true` if opened, `false` otherwise

python/src/exodusIIcpp.cpp

@@ -19,6 +19,7 @@ PYBIND11_MODULE(exodusIIcpp, m)
         .def(py::init())
         .def("open", &File::open)
         .def("create", &File::create)
+        .def("append", &File::append)
         .def("is_opened", &File::is_opened)
         .def("init", static_cast<void (File::*)()>(&File::init))
         .def("init",

src/file.cpp

@@ -105,6 +105,10 @@ File::File(exodusIIcpp::fs::path file_path, exodusIIcpp::FileAccess file_access)
         open(file_path.string());
         init();
     }
+    else if (file_access == exodusIIcpp::FileAccess::APPEND) {
+        append(file_path.string());
+        init();
+    }
     else
         create(file_path.string());
 }
@@ -137,6 +141,19 @@ File::create(const std::string & file_path)
         throw Exception(fmt::sprintf("Unable to open file '%s'.", file_path));
 }
 
+void
+File::append(const std::string & file_path)
+{
+    this->file_access = exodusIIcpp::FileAccess::APPEND;
+    this->exoid = ex_open(file_path.c_str(),
+                          EX_WRITE,
+                          &this->cpu_word_size,
+                          &this->io_word_size,
+                          &this->version);
+    if (this->exoid < 0)
+        throw Exception(fmt::sprintf("Unable to open file '%s'.", file_path));
+}
+
 bool
 File::is_opened() const
 {
@@ -146,7 +163,8 @@ File::is_opened() const
 void
 File::init()
 {
-    if (this->file_access == exodusIIcpp::FileAccess::READ) {
+    if (this->file_access == exodusIIcpp::FileAccess::READ ||
+        this->file_access == exodusIIcpp::FileAccess::APPEND) {
         char title[MAX_LINE_LENGTH + 1];
         memset(title, 0, sizeof(title));
         EXODUSIICPP_CHECK_ERROR(ex_get_init(this->exoid,

test/File_test.cpp

@@ -188,6 +188,80 @@ TEST(FileTest, create_edge2)
     EXPECT_EQ(g.get_num_side_sets(), 0);
 }
 
+TEST(FileTest, append_time_step)
+{
+    // Create initial file with one time step
+    {
+        File f(std::string("append_test.e"), FileAccess::WRITE);
+        EXPECT_TRUE(f.is_opened());
+        f.init("test", 2, 3, 1, 1, 0, 0);
+
+        std::vector<double> x = { 0, 1, 0 };
+        std::vector<double> y = { 0, 0, 1 };
+        f.write_coords(x, y);
+        f.write_coord_names();
+
+        std::vector<int> connect1 = { 1, 2, 3 };
+        f.write_block(1, "TRI3", 1, connect1);
+        std::vector<std::string> blk_names = { "blk1" };
+        f.write_block_names(blk_names);
+
+        f.write_time(1, 0.0);
+
+        std::vector<std::string> nv_names = { "nv1" };
+        f.write_nodal_var_names(nv_names);
+        f.write_nodal_var(1, 1, { 1.0, 2.0, 3.0 });
+
+        f.update();
+        f.close();
+    }
+
+    // Verify initial file has 1 time step
+    {
+        File f(std::string("append_test.e"), FileAccess::READ);
+        EXPECT_TRUE(f.is_opened());
+        f.read_times();
+        EXPECT_EQ(f.get_num_times(), 1);
+        f.close();
+    }
+
+    // Open with APPEND and add another time step
+    {
+        File f(std::string("append_test.e"), FileAccess::APPEND);
+        EXPECT_TRUE(f.is_opened());
+        f.read_times();
+        EXPECT_EQ(f.get_num_times(), 1);
+
+        // Write second time step
+        int next_step = f.get_num_times() + 1;
+        f.write_time(next_step, 1.0);
+        f.write_nodal_var(next_step, 1, { 2.0, 4.0, 6.0 });
+
+        f.update();
+        f.close();
+    }
+
+    // Verify file now has 2 time steps
+    {
+        File f(std::string("append_test.e"), FileAccess::READ);
+        EXPECT_TRUE(f.is_opened());
+        f.read_times();
+        EXPECT_EQ(f.get_num_times(), 2);
+
+        const std::vector<double> & times = f.get_times();
+        EXPECT_THAT(times, ElementsAre(DoubleEq(0.0), DoubleEq(1.0)));
+
+        // Verify variable values for both time steps
+        auto ts1_values = f.get_nodal_variable_values(1, 1);
+        EXPECT_THAT(ts1_values, ElementsAre(DoubleEq(1.0), DoubleEq(2.0), DoubleEq(3.0)));
+
+        auto ts2_values = f.get_nodal_variable_values(2, 1);
+        EXPECT_THAT(ts2_values, ElementsAre(DoubleEq(2.0), DoubleEq(4.0), DoubleEq(6.0)));
+
+        f.close();
+    }
+}
+
 TEST(FileTest, read_square)
 {
     File f(std::string(EXODUSIICPP_UNIT_TEST_ASSETS) + std::string("/square.e"), FileAccess::READ);