Fix Print::printf implementation

Author: tsl0922

cores/nRF5/Print.cpp

@@ -187,13 +187,19 @@ size_t Print::println(const Printable& x)
   return n;
 }
 
-int Print::printf(const char* format, ...)
+size_t Print::printf(const char * format, ...)
 {
-  va_list va;
-  va_start(va, format);
-  int ret = vprintf(format, va);
-  va_end(va);
-  return ret;
+  char buf[256];
+  int len;
+
+  va_list ap;
+  va_start(ap, format);
+
+  len = vsnprintf(buf, 256, format, ap);
+  this->write(buf, len);
+
+  va_end(ap);
+  return len;
 }
 
 // Private Methods /////////////////////////////////////////////////////////////

cores/nRF5/Print.h

@@ -83,7 +83,7 @@ class Print
     size_t println(double, int = 2);
     size_t println(const Printable&);
     size_t println(void);
-    int    printf(const char* format, ...) __attribute__ ((format (printf, 2, 3)));
+    size_t printf(const char* format, ...) __attribute__ ((format (printf, 2, 3)));
 
     virtual void flush() { /* Empty implementation for backward compatibility */ }