gistfile1.txt

static float sensor1 = 99.99;
static int sensor2 = 88;
static int sensor3 = 77;
static char sprintfbuffer[15];
static char dtostrfbuffer[6];

static char mergedbuffer[15];

void setup() {
  dtostrf(sensor1,5, 2, dtostrfbuffer);
  sprintf(sprintfbuffer, "%i,%i", sensor2, sensor3);
  
  memcpy(mergedbuffer, dtostrfbuffer, 5);
  *(mergedbuffer+5) = ',';
  memcpy(mergedbuffer+6, sprintfbuffer, 10);

  Serial.begin(9600);
  Serial.print("sprintfbuffer: ");
  Serial.println(sprintfbuffer);
  Serial.print("dtostrfbuffer: ");
  Serial.println(dtostrfbuffer);
  Serial.print("mergedbuffer: ");
  Serial.println(mergedbuffer);
}

void loop(){
}