How to convert String to Float

[Govs 0]

Hi, I'm using a launchpad and I want to convert a string value (weight) to a float or double value, have tried atof, but it doens't work. Do you know a way to achive this cast?

 

I have also tried float() or double(), like this:

 

String str="002.845";

float weight= float(str);

 

or

 

char str[7]="002.845";

double weight= atof(str);

[Fmilburn 445]

Hello @@Govs

 

You don't say in your post which LaunchPad you are using.  It is not documented on the Energia site but the toFloat() function works in Energia with the String class on at least some LaunchPads.

// Energia example using the toFloat() function with the String class
// Tested on MSP430F5529 and MSP430G2553 

void setup()
{
  Serial.begin(9600);
}
void loop()
{
  String pi;
  pi = "3.14153";
  double X = pi.toFloat();
  Serial.print("Pi = ");
  Serial.println(X, 5);
  
  while(1) {}
}

EDIT:  I should add that there was a really good series of posts on 43oh recently here on how the String class can get you in trouble on a microcontroller....

[B@tto 51]

String is evil

[yyrkoon 250]

atof() is another option.

 

const char *str ="123.456";

double d = atof(str);

 

Well assuming the Energia library has it. Which it seems so: https://github.com/energia/Energia/blob/master/hardware/msp430/cores/msp430/atof.h

[B@tto 51]

The problem is that to include atof() consume a lot of memory

[Fmilburn 445]

And yet another way if you are reading from the serial monitor in Energia is to use parseInt() and parseFloat() something like the following:

// Demostrates the use of Serial.parseInt and Serial.parseFloat in Energia
// Tested on MSP430F5529

void setup()
{
  Serial.begin(9600);
}

void loop()
{  
  Serial.println("Enter an integer... ");
  while(Serial.available() == 0) {
  }
  int a = Serial.parseInt();
  Serial.print("You entered: ");
  Serial.println(a); 
  
  Serial.println("Enter a floating point number... ");
  while(Serial.available() == 0) {
  }
  float b = Serial.parseFloat();
  Serial.print("You entered: ");
  Serial.println(;
}

[yyrkoon 250]

The problem is that to include atof() consume a lot of memory

Except, since it's in the Energia library already, I'm betting that's what .toFloat() is using . . . Either way, if you're *that* pressed for size, Energia might not be the best option . . .

[B@tto 51]

Energia or CCS it's the same problem as atof is a C library. 

[terjeio 134]

If you don't need a routine that supports a lot of different formats and need to have extensive error handling then it should be fairly easy to implement one.

 

This is what I did for integers:

int parseInt (char *s) {

	int c, res = 0, negative = 0;

	if(*s == '-') {
		negative = 1;
		s++;
	} else if(*s == '+')
		s++;

	while((c = *s++) != '\0') {
		if(c >= 48 && c <= 57)
			res = (res * 10) + c - 48;
	}

	return negative ? -res : res;

}

For decimals it is just finding the position of the decimal point and do a divison of the integer result?