Arduino sprintf float not formatting

Question

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 1

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.