support std::string with custom allocator

CHANGELOG.md

@@ -78,7 +78,8 @@
 - Simplified the log tags API. The `Tags` class has been removed. You now pass a `char const*` directly to the macros. Additionally, macros previously named `WITH_TAGS` have been renamed to `_TAGS`. For example, `LOG_INFO_WITH_TAGS` is now `LOG_INFO_TAGS`.
 - Renamed `backend_cpu_affinity` to `cpu_affinity` in `BackendOptions` to improve consistency.
 - Simplified project structure by removing the extra quill directory and made minor CMake improvements; `include/quill` is now directly in the root.
-
+- Added support for `std::string` with custom allocator ([#524](https://github.com/odygrd/quill/issues/524))
+
 ## v6.1.2
 
 - Fix pkg-config file on windows

include/quill/core/Codec.h

@@ -49,6 +49,17 @@ constexpr auto strnlen =
   ::strnlen
 #endif
   ;
+
+/** std string detection, ignoring the Allocator type **/
+template <typename T>
+struct is_std_string : std::false_type
+{
+};
+
+template <typename Allocator>
+struct is_std_string<std::basic_string<char, std::char_traits<char>, Allocator>> : std::true_type
+{
+};
 } // namespace detail
 
 /** typename = void for specializations with enable_if **/
@@ -75,7 +86,7 @@ struct Codec
       conditional_arg_size_cache.push_back(static_cast<size_t>(strlen(arg) + 1u));
       return conditional_arg_size_cache.back();
     }
-    else if constexpr (std::disjunction_v<std::is_same<Arg, std::string>, std::is_same<Arg, std::string_view>>)
+    else if constexpr (std::disjunction_v<detail::is_std_string<Arg>, std::is_same<Arg, std::string_view>>)
     {
       // for std::string we also need to store the size in order to correctly retrieve it
       // the reason for this is that if we create e.g:
@@ -126,7 +137,7 @@ struct Codec
       std::memcpy(buffer, arg, len);
       buffer += len;
     }
-    else if constexpr (std::disjunction_v<std::is_same<Arg, std::string>, std::is_same<Arg, std::string_view>>)
+    else if constexpr (std::disjunction_v<detail::is_std_string<Arg>, std::is_same<Arg, std::string_view>>)
     {
       // for std::string we store the size first, in order to correctly retrieve it
       // Copy the length first and then the actual string
@@ -170,7 +181,7 @@ struct Codec
       buffer += strlen(arg) + 1; // for c_strings we add +1 to the length as we also want to copy the null terminated char
       return arg;
     }
-    else if constexpr (std::disjunction_v<std::is_same<Arg, std::string>, std::is_same<Arg, std::string_view>>)
+    else if constexpr (std::disjunction_v<detail::is_std_string<Arg>, std::is_same<Arg, std::string_view>>)
     {
       // for std::string we first need to retrieve the length
       size_t len;
@@ -204,7 +215,7 @@ struct Codec
       // for std::string_view we would need fmt/format.h
       args_store->push_back(fmtquill::string_view{arg, strlen(arg)});
     }
-    else if constexpr (std::disjunction_v<std::is_same<Arg, std::string>, std::is_same<Arg, std::string_view>>)
+    else if constexpr (std::disjunction_v<detail::is_std_string<Arg>, std::is_same<Arg, std::string_view>>)
     {
       std::string_view arg = decode_arg(buffer);
 

test/integration_tests/StringLoggingTest.cpp

@@ -7,12 +7,49 @@
 #include "quill/sinks/FileSink.h"
 
 #include <cstdio>
+#include <memory>
 #include <string>
 #include <string_view>
 #include <vector>
 
 using namespace quill;
 
+template <typename T>
+class CustomAllocator : public std::allocator<T>
+{
+public:
+  using value_type = T;
+
+  CustomAllocator() noexcept : std::allocator<T>() {}
+
+  template <typename U>
+  explicit CustomAllocator(const CustomAllocator<U>& other) noexcept : std::allocator<T>(other)
+  {
+  }
+
+  [[nodiscard]] T* allocate(std::size_t n) { return std::allocator<T>::allocate(n); }
+
+  void deallocate(T* p, std::size_t n) noexcept { std::allocator<T>::deallocate(p, n); }
+
+  template <typename U>
+  struct rebind
+  {
+    using other = CustomAllocator<U>;
+  };
+};
+
+template <typename T, typename U>
+bool operator==(const CustomAllocator<T>&, const CustomAllocator<U>&)
+{
+  return true;
+}
+
+template <typename T, typename U>
+bool operator!=(const CustomAllocator<T>&, const CustomAllocator<U>&)
+{
+  return false;
+}
+
 /***/
 TEST_CASE("string_logging")
 {
@@ -39,6 +76,8 @@ TEST_CASE("string_logging")
   Logger* logger = Frontend::create_or_get_logger(logger_name, std::move(file_sink));
 
   {
+    std::basic_string<char, std::char_traits<char>, CustomAllocator<char>> cas =
+      "custom allocator string";
     std::string s = "adipiscing";
     std::string const& scr = s;
     std::string& sr = s;
@@ -62,6 +101,7 @@ TEST_CASE("string_logging")
     const char* npcs = "Example\u0003String\u0004";
     LOG_INFO(logger, "non printable cs [{}]", npcs);
 
+    LOG_INFO(logger, "cas [{}]", cas);
     LOG_INFO(logger, "s [{}]", s);
     LOG_INFO(logger, "scr [{}]", scr);
     LOG_INFO(logger, "sr [{}]", sr);
@@ -110,7 +150,10 @@ TEST_CASE("string_logging")
 
   // Read file and check
   std::vector<std::string> const file_contents = quill::testing::file_contents(filename);
-  REQUIRE_EQ(file_contents.size(), number_of_messages + 15);
+  REQUIRE_EQ(file_contents.size(), number_of_messages + 16);
+
+  REQUIRE(quill::testing::file_contains(
+    file_contents, std::string{"LOG_INFO      " + logger_name + "       cas [custom allocator string]"}));
 
   REQUIRE(quill::testing::file_contains(
     file_contents, std::string{"LOG_INFO      " + logger_name + "       non printable cs [Example\\x03String\\x04]"}));