🚑 fix for #465

src/json.hpp

@@ -8310,16 +8310,7 @@ class basic_json
             static_assert(d == 6 or d == 15 or d == 16 or d == 17,
                           "unexpected NumberType");
 
-            static constexpr auto fmt = d == 6  ? "%.7g"
-                                        : d == 15 ? "%.16g"
-                                        : d == 16 ? "%.17g"
-                                        : d == 17 ? "%.18g"
-                                        :           "%.19g";
-            // I'm not sure why we need to +1 the precision,
-            // but without it there's a unit-test that fails
-            // that asserts precision of the output
-
-            snprintf(m_buf.data(), m_buf.size(), fmt, x);
+            snprintf(m_buf.data(), m_buf.size(), "%.*g", d, x);
 
             // read information from locale
             const auto loc = localeconv();

src/json.hpp.re2c

@@ -8310,16 +8310,7 @@ class basic_json
             static_assert(d == 6 or d == 15 or d == 16 or d == 17,
                           "unexpected NumberType");
 
-            static constexpr auto fmt = d == 6  ? "%.7g"
-                                        : d == 15 ? "%.16g"
-                                        : d == 16 ? "%.17g"
-                                        : d == 17 ? "%.18g"
-                                        :           "%.19g";
-            // I'm not sure why we need to +1 the precision,
-            // but without it there's a unit-test that fails
-            // that asserts precision of the output
-
-            snprintf(m_buf.data(), m_buf.size(), fmt, x);
+            snprintf(m_buf.data(), m_buf.size(), "%.*g", d, x);
 
             // read information from locale
             const auto loc = localeconv();

test/src/unit-inspection.cpp

@@ -250,17 +250,31 @@ TEST_CASE("object inspection")
             ss.str(std::string());
 
             // use stringstream for JSON serialization
-            json j_number = 3.141592653589793;
+            json j_number = 3.14159265358979;
             ss << j_number;
 
             // check that precision has been overridden during serialization
-            CHECK(ss.str() == "3.141592653589793");
+            CHECK(ss.str() == "3.14159265358979");
 
             // check that precision has been restored
             CHECK(ss.precision() == 3);
         }
     }
 
+    SECTION("round trips")
+    {
+        for (const auto& s :
+    {"3.141592653589793", "1000000000000000010E5"
+    })
+        {
+            json j1 = json::parse(s);
+            std::string s1 = j1.dump();
+            json j2 = json::parse(s1);
+            std::string s2 = j2.dump();
+            CHECK(s1 == s2);
+        }
+    }
+
     SECTION("return the type of the object (explicit)")
     {
         SECTION("null")

test/src/unit-regression.cpp

@@ -783,4 +783,13 @@ TEST_CASE("regression tests")
         json j = R"({"bool_value":true,"double_value":2.0,"int_value":10,"level1":{"list_value":[3,"hi",false],"tmp":5.0},"string_value":"hello"})"_json;
         CHECK(j["double_value"].is_number_float());
     }
+
+    SECTION("issue #465 - roundtrip error while parsing 1000000000000000010E5")
+    {
+        json j1 = json::parse("1000000000000000010E5");
+        std::string s1 = j1.dump();
+        json j2 = json::parse(s1);
+        std::string s2 = j2.dump();
+        CHECK(s1 == s2);
+    }
 }