Arduino sprintf float not formatting

问题:

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.

回答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.

回答2:

As has been stated before Float support is not included in sprintf on Arduino.

String class

Arduino has its own String class.

String value = String(3.14);

then,

char *result = value.c_str();

String class reference, link above

Constructs an instance of the String class. There are multiple versions that construct Strings from different data types (i.e. format them as sequences of characters), including:

• a constant string of characters, in double quotes (i.e. a char array)
• a single constant character, in single quotes
• another instance of the String object
• a constant integer or long integer
• a constant integer or long integer, using a specified base
• an integer or long integer variable
• an integer or long integer variable, using a specified base
• a float or double, using a specified decimal palces