Arduino sprintf float not formatting

c++ arduino printf
Mistergreen picture Mistergreen · Dec 25, 2014 · Viewed 65.2k times · Source

I have this arduino sketch,

char temperature[10];
float temp = 10.55;
sprintf(temperature,"%f F", temp);
Serial.println(temperature);

temperature prints out as

? F

Any thoughts on how to format this float? I need it to be a char string.

Answer

Dinal24 picture Dinal24 · Dec 26, 2014

Due to some performance reasons %f is not included in the Arduino's implementation of sprintf(). A better option would be to use dtostrf() - you convert the floating point value to a C-style string, Method signature looks like:

char *dtostrf(double val, signed char width, unsigned char prec, char *s)

Use this method to convert it to a C-Style string and then use sprintf, eg:

char str_temp[6];

/* 4 is mininum width, 2 is precision; float value is copied onto str_temp*/
dtostrf(temp, 4, 2, str_temp);
sprintf(temperature,"%s F", str_temp);

You can change the minimum width and precision to match the float you are converting.

Related questions

Does Arduino use C or C++?

Coming from Python, the whole C/C++ thing is kind of alien to begin with... and then I see in one place that Arduino uses 'standard' C, and in another that it uses 'standard' C++, so on and so forth. …

Read More
How to program an Arduino with C++

So lately I've been playing around with my Arduino and I was wondering if there was some way I could program the Arduino in C++. I've been programming it using the C++/Processing language in Vim and using a makefile …

Read More
Vectors in Arduino

I am making a vector of "waypoints" on the Arduino. Each waypoint is an object. The Arduino will obviously need to store multiple waypoints for waypoint navigation. But instead of storing these waypoints in a standard preprogrammed array, the user …

Read More