Merge pull request zerebubuth#390 from mmd-osm/patch/jsonentryint

json writer: fmt for formatting integer values

Author: mmd-osm

include/cgimap/json_writer.hpp

@@ -10,11 +10,16 @@
 #ifndef JSON_WRITER_HPP
 #define JSON_WRITER_HPP
 
+#include <array>
 #include <memory>
 #include <string>
 #include <string_view>
 #include <stdexcept>
+
+#include <fmt/core.h>
+#include <fmt/compile.h>
 #include <yajl/yajl_gen.h>
+
 #include "cgimap/output_buffer.hpp"
 #include "cgimap/output_writer.hpp"
 
@@ -46,7 +51,26 @@ class json_writer : public output_writer {
 
   template<typename TInteger, std::enable_if_t<std::is_integral_v<TInteger>, bool> = true>
   void entry(TInteger i) {
-    yajl_gen_integer(gen, i);
+
+    const char* str = nullptr;
+    size_t len = 0;
+
+  #if FMT_VERSION >= 90000
+    std::array<char, 64> buf;
+    constexpr size_t max_chars = buf.size() - 1;
+    auto [end, n_written] = fmt::format_to_n(buf.begin(), max_chars, FMT_COMPILE("{:d}"), i);
+    if (n_written > max_chars)
+      throw write_error("cannot convert int attribute to string.");
+    *end = '\0'; // Null terminate string
+    str = buf.data();
+    len = n_written;
+  #else
+    auto s = fmt::format("{:d}", i);
+    str = s.c_str();
+    len = s.length();
+  #endif
+
+    yajl_gen_number(gen, str, len);
   }
 
   void entry(const char* s);