From 68a21c5a5952913d6192be747efd245887bc36cc Mon Sep 17 00:00:00 2001
From: Alexis Placet <2400067+Alex-PLACET@users.noreply.github.com>
Date: Thu, 30 Apr 2026 13:24:54 +0200
Subject: [PATCH 1/2] Fix substring calculation in CSV cell parsing and add
 lexical_cast for signed and unsigned char

---
 include/xtensor/io/xcsv.hpp | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/include/xtensor/io/xcsv.hpp b/include/xtensor/io/xcsv.hpp
index 080ccaf54..2fd347745 100644
--- a/include/xtensor/io/xcsv.hpp
+++ b/include/xtensor/io/xcsv.hpp
@@ -66,7 +66,7 @@ namespace xt
             }
 
             size_t last = cell.find_last_not_of(' ');
-            return cell.substr(first, last == std::string::npos ? cell.size() : last + 1);
+            return cell.substr(first, last == std::string::npos ? cell.size() : last - first + 1);
         }
 
         template <>
@@ -93,6 +93,18 @@ namespace xt
             return std::stoi(cell);
         }
 
+        template <>
+        inline signed char lexical_cast<signed char>(const std::string& cell)
+        {
+            return static_cast<signed char>(std::stoi(cell));
+        }
+
+        template <>
+        inline unsigned char lexical_cast<unsigned char>(const std::string& cell)
+        {
+            return static_cast<unsigned char>(std::stoul(cell));
+        }
+
         template <>
         inline long lexical_cast<long>(const std::string& cell)
         {

From 136374ea24436cdb173f3fde16215c798f33aa54 Mon Sep 17 00:00:00 2001
From: Alexis Placet <2400067+Alex-PLACET@users.noreply.github.com>
Date: Tue, 5 May 2026 09:36:55 +0200
Subject: [PATCH 2/2] Add CSV dumping functionality with configurable
 delimiters

Co-authored-by: Copilot <copilot@github.com>
---
 include/xtensor/io/xcsv.hpp | 45 +++++++++++++++++++++++++++++++++++--
 test/test_xcsv.cpp          | 24 ++++++++++++++++++++
 2 files changed, 67 insertions(+), 2 deletions(-)

diff --git a/include/xtensor/io/xcsv.hpp b/include/xtensor/io/xcsv.hpp
index 2fd347745..70472625e 100644
--- a/include/xtensor/io/xcsv.hpp
+++ b/include/xtensor/io/xcsv.hpp
@@ -274,6 +274,47 @@ namespace xt
         }
     };
 
+    template <class E>
+    void dump_csv(std::ostream& stream, const xexpression<E>& e, const xcsv_config& config)
+    {
+        using size_type = typename E::size_type;
+        const E& ex = e.derived_cast();
+        if (ex.dimension() == 1)
+        {
+            const size_type n = ex.shape()[0];
+            for (size_type i = 0; i != n; ++i)
+            {
+                stream << ex(i);
+                if (i != n - 1)
+                {
+                    stream << config.delimiter;
+                }
+            }
+            stream << std::endl;
+        }
+        else if (ex.dimension() == 2)
+        {
+            const size_type nbrows = ex.shape()[0];
+            const size_type nbcols = ex.shape()[1];
+            for (size_type r = 0; r != nbrows; ++r)
+            {
+                for (size_type c = 0; c != nbcols; ++c)
+                {
+                    stream << ex(r, c);
+                    if (c != nbcols - 1)
+                    {
+                        stream << config.delimiter;
+                    }
+                }
+                stream << std::endl;
+            }
+        }
+        else
+        {
+            XTENSOR_THROW(std::runtime_error, "Only 1-D and 2-D expressions can be serialized to CSV");
+        }
+    }
+
     template <class E>
     void load_file(std::istream& stream, xexpression<E>& e, const xcsv_config& config)
     {
@@ -287,9 +328,9 @@ namespace xt
     }
 
     template <class E>
-    void dump_file(std::ostream& stream, const xexpression<E>& e, const xcsv_config&)
+    void dump_file(std::ostream& stream, const xexpression<E>& e, const xcsv_config& config)
     {
-        dump_csv(stream, e);
+        dump_csv(stream, e, config);
     }
 }
 
diff --git a/test/test_xcsv.cpp b/test/test_xcsv.cpp
index 148b40cd3..00fcd4519 100644
--- a/test/test_xcsv.cpp
+++ b/test/test_xcsv.cpp
@@ -162,4 +162,28 @@ namespace xt
 
         XT_EXPECT_THROW(dump_csv(res, data), std::runtime_error);
     }
+
+    TEST(xcsv, dump_with_config)
+    {
+        xtensor<double, 2> data{{1.0, 2.0, 3.0, 4.0}, {10.0, 12.0, 15.0, 18.0}};
+
+        std::stringstream res;
+
+        xcsv_config config;
+        config.delimiter = ' ';
+        dump_csv(res, data, config);
+        ASSERT_EQ("1 2 3 4\n10 12 15 18\n", res.str());
+    }
+
+    TEST(xcsv, dump_file_with_config)
+    {
+        xtensor<double, 2> data{{1.0, 2.0, 3.0, 4.0}, {10.0, 12.0, 15.0, 18.0}};
+
+        std::stringstream res;
+
+        xcsv_config config;
+        config.delimiter = ';';
+        dump_file(res, data, config);
+        ASSERT_EQ("1;2;3;4\n10;12;15;18\n", res.str());
+    }
 }