Merge branch 'cxx20'

Fix C++20 build and test it in the CI.

See #1340.

.github/workflows/ci.yml

@@ -121,6 +121,7 @@ jobs:
             backend: Valgrind
             runner: ubuntu-24.04
             name: Valgrind
+            cxxstd: 20
           - lib_type: shared
             backend: MySQL
             runner: ubuntu-24.04

include/soci/error.h

@@ -22,6 +22,12 @@ class SOCI_DECL soci_error : public std::runtime_error
 public:
     explicit soci_error(std::string const & msg);
 
+    // Provide a simple way to construct the message from a format (using fmt
+    // syntax, i.e. with {} placeholders) and one argument of the given type.
+    soci_error(char const* format, std::string const& arg);
+    soci_error(char const* format, int arg);
+    soci_error(char const* format, size_t arg);
+
     soci_error(soci_error const& e) noexcept;
     soci_error& operator=(soci_error const& e) noexcept;
 
@@ -71,7 +77,7 @@ public:
 
 private:
     // Optional extra information (currently just the context data).
-    class soci_error_extra_info* info_;
+    class soci_error_extra_info* info_ = nullptr;
 };
 
 } // namespace soci

include/soci/fmt.h

@@ -1,24 +0,0 @@
-//
-// Copyright (C) 2026 Vadim Zeitlin
-// Distributed under the Boost Software License, Version 1.0.
-// (See accompanying file LICENSE_1_0.txt or copy at
-// https://www.boost.org/LICENSE_1_0.txt)
-//
-
-#ifndef SOCI_FMT_H_INCLUDED
-#define SOCI_FMT_H_INCLUDED
-
-#include <string>
-
-namespace soci
-{
-
-// Export a couple of overloads of format() used in public headers to allow
-// using them there without requiring including fmt headers.
-std::string SOCI_DECL format(const char* fmt, std::string const& arg);
-std::string SOCI_DECL format(const char* fmt, int arg);
-std::string SOCI_DECL format(const char* fmt, size_t arg);
-
-} // namespace soci
-
-#endif // SOCI_FMT_H_INCLUDED

include/soci/type-holder.h

@@ -10,7 +10,6 @@
 
 #include "soci/blob.h"
 #include "soci/error.h"
-#include "soci/fmt.h"
 #include "soci/soci-backend.h"
 #include "soci/soci-types.h"
 
@@ -486,7 +485,7 @@ private:
         }
 
         // This should be unreachable
-        throw soci_error(format("Created holder with unsupported type {}", static_cast<int>(dt)));
+        throw soci_error("Created holder with unsupported type {}", static_cast<int>(dt));
     }
 
     const db_type dt_;

include/soci/values.h

@@ -11,7 +11,6 @@
 #include "soci/statement.h"
 #include "soci/into-type.h"
 #include "soci/use-type.h"
-#include "soci/fmt.h"
 // std
 #include <cstddef>
 #include <map>
@@ -67,7 +66,7 @@ public:
         }
         else
         {
-            throw soci_error(format("Column at position {} contains NULL value and no default was provided", pos));
+            throw soci_error("Column at position {} contains NULL value and no default was provided", pos);
         }
     }
 
@@ -124,7 +123,7 @@ public:
         }
         else
         {
-            throw soci_error(format("Column at position {} contains NULL value and no default was provided", currentPos_));
+            throw soci_error("Column at position {} contains NULL value and no default was provided", currentPos_);
         }
 
         return *this;
@@ -290,7 +289,7 @@ private:
         }
         else
         {
-            throw soci_error(format("Value at position {} was set using a different type than the one passed to get()", pos));
+            throw soci_error("Value at position {} was set using a different type than the one passed to get()", pos);
         }
     }
 

src/core/CMakeLists.txt

@@ -72,7 +72,6 @@ target_sources(soci_core
       "${PROJECT_SOURCE_DIR}/include/soci/error.h"
       "${PROJECT_SOURCE_DIR}/include/soci/exchange-traits.h"
       "${PROJECT_SOURCE_DIR}/include/soci/fixed-size-ints.h"
-      "${PROJECT_SOURCE_DIR}/include/soci/fmt.h"
       "${PROJECT_SOURCE_DIR}/include/soci/into-type.h"
       "${PROJECT_SOURCE_DIR}/include/soci/into.h"
       "${PROJECT_SOURCE_DIR}/include/soci/is-detected.h"

src/core/common.cpp

@@ -7,14 +7,11 @@
 //
 
 #include "soci/error.h"
-#include "soci/fmt.h"
 #include "soci-mktime.h"
 #include <climits>
 #include <cstdlib>
 #include <ctime>
 
-#include <fmt/format.h>
-
 namespace // anonymous
 {
 
@@ -140,18 +137,3 @@ time_t soci::details::timegm_impl_soci ( struct tm* tb )
 
     return since_epoch;
 }
-
-std::string soci::format(const char* fmt, std::string const& arg)
-{
-    return fmt::format(fmt, arg);
-}
-
-std::string soci::format(const char* fmt, int arg)
-{
-    return fmt::format(fmt, arg);
-}
-
-std::string soci::format(const char* fmt, size_t arg)
-{
-    return fmt::format(fmt, arg);
-}

src/core/error.cpp

@@ -10,6 +10,8 @@
 
 #include <vector>
 
+#include <fmt/format.h>
+
 namespace soci
 {
 
@@ -95,7 +97,21 @@ soci_error_extra_info *make_safe_copy(soci_error_extra_info* info)
 soci_error::soci_error(std::string const & msg)
      : std::runtime_error(msg)
 {
-    info_ = nullptr;
+}
+
+soci_error::soci_error(char const* format, std::string const& arg)
+    : std::runtime_error(fmt::vformat(format, fmt::make_format_args(arg)))
+{
+}
+
+soci_error::soci_error(char const* format, int arg)
+    : std::runtime_error(fmt::vformat(format, fmt::make_format_args(arg)))
+{
+}
+
+soci_error::soci_error(char const* format, size_t arg)
+    : std::runtime_error(fmt::vformat(format, fmt::make_format_args(arg)))
+{
 }
 
 soci_error::soci_error(soci_error const& e) noexcept