float to string ?

Using Arduino Programming Questions
1

Hello I work with a "STRING" problem.
I need to send some data to my server which will be packaged together in a string with ID data and link file name.
I've simplified the code to the problem.

If I use "int testc = 25" so it works although without decimals.
I must, however, use decimals to a calculation.
but if I use "float testc = 25.65".
Become the result nonsense.

I think that my problem has something to do with %c to do.
but I'm not sure.

#include <SPI.h>

char * dst;
char data[0xff];
float testc=25.65;


void setup()
{
  Serial.begin(9600);

}

void loop()
{
  Serial.println(testc);// Test out put.

  strcpy(data,"/test_fil_1_ok_3.php?id=test444&temp=");
  dst = data + strlen(data);
  dst += sprintf(dst, "%c", testc);
  Serial.println(data);
  delay (10000);

  
}

Does anyone have an idea.
best Kim Jessen

2

%c specifies to print the data as an ASCII char. If you want to print as a floating point value, use %f.

Regards,
Ray L.

3

Except that there isn't support for %f in the arduino. The easiest way is to convert the float to a string first with dtostrf and then use sprintf with that string already as a string.

4

Delta_G:
Except that there isn't support for %f in the arduino. The easiest way is to convert the float to a string first with dtostrf and then use sprintf with that string already as a string.

Didn't know that - never used Arduino printf/sprintf. Yet another way to do it is:

dst += sprintf(dst, "%d.%d", (int)testc, (int)((testc - (int)testc) * 1000.0));

This also lets you specify the number of decimal points that get printed.

Regards,
Ray L.

5

Try:

dtostrf(float floatvar, int StringLengthIncDecimalPoint, int numVarsAfterDecimal, char charbuf[]);
6

RayLivingston:
Didn't know that - never used Arduino printf/sprintf. Yet another way to do it is:

dst += sprintf(dst, "%d.%d", (int)testc, (int)((testc - (int)testc) * 1000.0));

This also lets you specify the number of decimal points that get printed.

...but suffers from leading zero suppression in the fraction.

7

hey Ray L,
It works many thanks for the help

8

kimjessen:
hey Ray L,
It works many thanks for the help

Try printing 1.5 and 1.05

9

AWOL:
...but suffers from leading zero suppression in the fraction.

OK, then:

dst += sprintf(dst, "%d.%03d", (int)testc, (int)((testc - (int)testc) * 1000.0));

Or does Arduino sprintf also not support length specifiers?

Regards,
Ray L.

10

RayLivingston:
does Arduino sprintf also not support length specifiers?

It does, I'v tried :stuck_out_tongue:

11