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--- guides:common_coding_errors_payload_testing [2012/08/28 11:57] – danielrichman
+++ guides:common_coding_errors_payload_testing [2012/10/09 18:54] (current) – [Prime Meridian] danielrichman
@@ Line 18: / Line 18: @@
 char s[30];
 double lat = 54.086611;
-dstrtof(lat, 8, 6, s); // == "54.086611"
+dtostrf(lat, 8, 6, s); // == "54.086611"
 </code>
@@ Line 27: / Line 27: @@
 </code>
-Unfortunately the second one might not always compile. With limited memory on a typical microcontroller, the printf() series of functions in [[http://www.nongnu.org/avr-libc/|AVR Libc]] (used by Arduino) do not by default support printing of floating point values using the %f operator. You can enable floating point support in printf, though it's difficult and requires memory.
+Unfortunately the second one might not always compile. With limited memory on a typical microcontroller, the printf() series of functions in [[http://www.nongnu.org/avr-libc/|AVR Libc]] (used by Arduino) do not by default support printing of floating point values using the %f operator. You can enable floating point support in printf, though it's difficult.
 ==== The hard way ====
@@ Line 91: / Line 91: @@
 <code c>long i2 = labs(lround((lon - i1) * 1000000)); // == 1234</code>
+There's another case to consider. Clearly the idea is to split the float into the an integer and a fraction of an integer (i1 and i2 respectively).
+The intention is the above code is that the integer part will supply the negative sign if required. However, consider -0.7. i1 would be -0, but -0 == 0, and the result would be "0.7". We'll have to handle negative numbers explicitly:
+<code c>snprintf(where, buf_size, "%s%i.%06li", (what < 0 ? "-" : ""), labs(i1), i2);</code>
 ==== Equatorial ====
-Theoretically the Equator not really an issue for us but worth mentioning for our Kenyan viewers. Really, you should place your float to string code in a separate function and call it for latitude and longitude. This also means that this function can be unit tested.
+Practically the Equator is not really an issue for us but worth mentioning for our Kenyan viewers. Really, you should place your float to string code in a separate function and call it for latitude and longitude. This also means that this function can be unit tested.
 ==== Fixed version ====
@@ Line 107: / Line 114: @@
     int i1 = what;
     long i2 = labs(lround((what - i1) * 1000000));
-    snprintf(where, buf_size, "%i.%06li", i1, i2);
+    snprintf(where, buf_size, "%s%i.%06li", (what < 0 ? "-" : ""), labs(i1), i2);
 }