Add String::format()

Author: matsujirushi

cores/arduino/WString.cpp

@@ -22,6 +22,8 @@
 #include "WString.h"
 #include "itoa.h"
 #include "avr/dtostrf.h"
+#include <stdio.h>
+#include <stdarg.h>
 
 /*********************************************/
 /*  Constructors                             */
@@ -126,6 +128,18 @@ String::~String()
 	free(buffer);
 }
 
+String String::format(const char* format, ...)
+{
+	va_list arg;
+	va_start(arg, format);
+	const int len = vsnprintf(nullptr, 0, format, arg);
+	char str[len + 1];
+	vsnprintf(str, sizeof(str), format, arg);
+	va_end(arg);
+
+	return String(str);
+}
+
 /*********************************************/
 /*  Memory Management                        */
 /*********************************************/

cores/arduino/WString.h

@@ -73,6 +73,8 @@ class String
 	explicit String(double, unsigned char decimalPlaces=2);
 	~String(void);
 
+	static String format(const char* format, ...);
+
 	// memory management
 	// return true on success, false on failure (in which case, the string
 	// is left unchanged).  reserve(0), if successful, will validate an