Extracted class StringBuilder

JsonGeneratorTests/JsonArray.cpp

@@ -3,6 +3,4 @@
 * Benoit Blanchon 2014 - MIT License
 */
 
-#include <string.h>
-
 #include "JsonArray.h"

JsonGeneratorTests/JsonArray.h

@@ -5,7 +5,7 @@
 
 #pragma once
 
-#include <stdarg.h>
+#include "StringBuilder.h"
 
 enum JsonObjectType
 {
@@ -67,14 +67,22 @@ public:
 
     void writeTo(char* buffer, size_t bufferSize)
     {
-        buffer[0] = 0;
+        StringBuilder sb(buffer, bufferSize);
+        writeTo(sb);
+    }
 
-        append(buffer, bufferSize, "[");
+private:
+    JsonObject items[N];
+    int itemCount;
+
+    void writeTo(StringBuilder& sb)
+    {
+        sb.append("[");
 
         for (int i = 0; i < itemCount; i++)
         {
             if (i>0)
-                append(buffer, bufferSize, ",");
+                sb.append(",");
 
             JsonObjectValue value = items[i].value;
 
@@ -82,36 +90,22 @@ public:
             {
             case JSON_STRING:
                 if (value.string)
-                    append(buffer, bufferSize, "\"%s\"", value.string);
+                    sb.append("\"%s\"", value.string);
                 else
-                    append(buffer, bufferSize, "null");
+                    sb.append("null");
                 break;
 
             case JSON_NUMBER:
-                append(buffer, bufferSize, "%lg", value.number);
+                sb.append("%lg", value.number);
                 break;
 
             case JSON_BOOLEAN:
-                append(buffer, bufferSize, value.boolean ? "true" : "false");
+                sb.append(value.boolean ? "true" : "false");
                 break;
             }
         }
 
-        append(buffer, bufferSize, "]");
-    }
-
-private:
-    JsonObject items[N];
-    int itemCount;
-
-    void append(char* dest, size_t destSize, const char* format, ...)
-    {
-        int len = strlen(dest);
-
-        va_list args;
-        va_start(args, format);
-        vsnprintf(dest + len, destSize - len, format, args);
-        va_end(args);
+        sb.append("]");
     }
 };
 

JsonGeneratorTests/JsonGeneratorTests.vcxproj

@@ -84,9 +84,11 @@
   <ItemGroup>
     <ClCompile Include="JsonArray.cpp" />
     <ClCompile Include="JsonArrayTests.cpp" />
+    <ClCompile Include="StringBuilder.cpp" />
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="JsonArray.h" />
+    <ClInclude Include="StringBuilder.h" />
   </ItemGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
   <ImportGroup Label="ExtensionTargets">

JsonGeneratorTests/JsonGeneratorTests.vcxproj.filters

@@ -21,10 +21,16 @@
     <ClCompile Include="JsonArray.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="StringBuilder.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="JsonArray.h">
       <Filter>Header Files</Filter>
     </ClInclude>
+    <ClInclude Include="StringBuilder.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
   </ItemGroup>
 </Project>

JsonGeneratorTests/StringBuilder.cpp

@@ -0,0 +1,14 @@
+#include "StringBuilder.h"
+
+
+void StringBuilder::append(const char* format, ...)
+{
+    char* tail = buffer + length;
+
+    va_list args;
+    va_start(args, format);
+    vsnprintf(tail, capacity - length, format, args);
+    va_end(args);
+
+    length += strlen(tail);
+}

JsonGeneratorTests/StringBuilder.h

@@ -0,0 +1,27 @@
+/*
+ * Arduino JSON library
+ * Benoit Blanchon 2014 - MIT License
+ */
+
+#pragma once
+
+#include <cstdarg>
+#include <cstdio>
+#include <cstring>
+
+class StringBuilder
+{
+public:
+    StringBuilder(char* buf, size_t size)
+        : buffer(buf), capacity(size), length(0)
+    {
+    }
+
+    void append(const char* format, ...);
+
+private:
+    char* buffer;
+    int capacity;
+    int length;
+};
+