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added 1084 characters in body

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edited May 4, 2016 at 14:50

EDIT

After trying to use the @Majenko's answer I sometimes get garbage values printed. Any ideas why?

float a = analogRead(A1) / 1023.;
float b = analogRead(A2) / 1023.;
bool c = analogRead(A3) / 1023;

char* output = createString(a, b, c);
Serial.println(output);


char* createString (float _a, float _b, bool _c) 
{
    char a_string[5];
    dtostrf(_a, 4, 1, a_string);
    
    char b_string[5];
    dtostrf(_b, 4, 1, b_string);
    
    char out[12];
    snprintf(out, 12, "%4s %4s %d", a_string, b_string, c ? 1 : 0);
    return out;
}

and the output:

 0.6  1.0 0
 0.6  1.0 0
 0.6  1.0 0
 0.6  1.0 0
 0.6  1.0 0
 0.6  1.0 0
 0.�tS
�
 0.6  `S
�
 0.6  1.0
}
 0.6  1.0 0
 0.7  1.0 0
 0.6  1.0 0
 0.6  1.0 0

using

  Serial.print(a_string);
  Serial.print(" ");
  Serial.print(b_string);
  Serial.print(" ");
  Serial.println(c);

doesn't produce the errors

EDIT

After trying to use the @Majenko's answer I sometimes get garbage values printed. Any ideas why?

float a = analogRead(A1) / 1023.;
float b = analogRead(A2) / 1023.;
bool c = analogRead(A3) / 1023;

char* output = createString(a, b, c);
Serial.println(output);


char* createString (float _a, float _b, bool _c) 
{
    char a_string[5];
    dtostrf(_a, 4, 1, a_string);
    
    char b_string[5];
    dtostrf(_b, 4, 1, b_string);
    
    char out[12];
    snprintf(out, 12, "%4s %4s %d", a_string, b_string, c ? 1 : 0);
    return out;
}

and the output:

 0.6  1.0 0
 0.6  1.0 0
 0.6  1.0 0
 0.6  1.0 0
 0.6  1.0 0
 0.6  1.0 0
 0.�tS
�
 0.6  `S
�
 0.6  1.0
}
 0.6  1.0 0
 0.7  1.0 0
 0.6  1.0 0
 0.6  1.0 0

using

  Serial.print(a_string);
  Serial.print(" ");
  Serial.print(b_string);
  Serial.print(" ");
  Serial.println(c);

doesn't produce the errors

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asked Apr 25, 2016 at 18:30

waspinator

build fixed size strings from floats

This is likely a duplicate, but I couldn't find the original question. This is really basic, but just can't figure it out.

I'm trying to combine a few char arrays together. This is what I've tried so far.

float a = 12.3456;
float b = 5.4321;
bool c = true;

char a_string[4];
dtostrf(a, 4, 1, a_string);

char b_string[4];
dtostrf(b, 4, 1, b_string);

char c_string[2] = {'0', '\0'};
if (c) {
  c_string[0] = '1';
}

char output[12] = "-----------";

output[0] = a_string[0];
output[1] = a_string[1];
output[2] = a_string[2];
output[3] = a_string[3];

output[4] = ' ';

output[5] = b_string[0];
output[6] = b_string[1];
output[7] = b_string[2];
output[8] = b_string[3];

output[9] = ' ';

output[10] = c_string[0];

Serial.println(output);

Results in an empty string in seems.

If I remove the second dtostrf(), and change b_string[0] ... to a_string[0] Then I get 12.3 12.3 1. Doesn't seem to like having dtostrf() called more than once, but it seems like the function I want, since it allows me to set a fixed strint size. The output I'd be looking for is 12.3 5.4 1

another approach

String a_string = String(a, 1);
String b_string = String(b, 1);
String c_string = String(c);

String output;
String space = " ";

output.concat(a_string);
output.concat(space);
output.concat(b_string);
output.concat(space);
output.concat(c_string);

Serial.println(output);

This outputs 12.3 5.4 1. Is there a way to make the String fixed width? I'm looking for

12.3 5.4 1 instead of

12.3 5.4 1

What's the proper way of doing this?

string float