fix

cores/esp8266/core_esp8266_noniso.cpp

@@ -41,17 +41,6 @@ char* ultoa(unsigned long value, char* result, int base) {
  return utoa((unsigned int)value, result, base);
 }
 
-char * dtostrf(double number, signed char width, unsigned char prec, char *s) {
- if (!_printf_float) {
- return __dtostrf(number, width, prec, s);
- } else {
- char fmt[32];
- sprintf(fmt, "%%%d.%df", width, prec);
- sprintf(s, fmt, number);
- return s;
- }
-}
-
 static char * __dtostrf(double number, signed char width, unsigned char prec, char *s) {
  bool negative = false;
 
@@ -129,4 +118,18 @@ static char * __dtostrf(double number, signed char width, unsigned char prec, ch
  return s;
 }
 
+// extern weak declaration (= function pointer) to check whether _printf_float is defined
+extern int _printf_float () __attribute__((__weak__));
+
+char * dtostrf(double number, signed char width, unsigned char prec, char *s) {
+ if (!_printf_float) {
+ return __dtostrf(number, width, prec, s);
+ } else {
+ char fmt[32];
+ sprintf(fmt, "%%%d.%df", width, prec);
+ sprintf(s, fmt, number);
+ return s;
+ }
+}
+
 };