Question about using array with sprintf() to send file to sd and to cloud

Projects Programming
1

Hi,

I would like to ask for some help. I want extend my code. Now I am writing temperature values to array ( for example char pageadd[128] ) with sprintf.
Than sending it to the cloud and also to SD card:

sprintf(pageAdd,"/update?key=XXXXXXXXXXXXX&field1=%i&field2=%i&field3=%i&field4=%i&field5=%i",temp0,temp1,temp2,temp3,temp4);
if(!getPage(server,pageAdd)) Serial.print(F("Fail "));
 else Serial.print(F("Pass "));

defining logfile and sending to SD:

int logFile(char* sdate, char* stime, int temp0, int temp1, int temp2, int temp3, int temp4) {
 
  File fh = SD.open("xyz.txt",FILE_WRITE);
  if(!fh) {
    Serial.println(F("Open fail"));
    return 0;
  }

  sprintf(pageAdd,"%s,%s,%i,%i,%i,%i,%i;",sdate,stime,temp0,temp1,temp2,temp3,temp4);
 
  fh.println(pageAdd);
  fh.close();
  return 1;

This cloud cannot handle more than 8 fields for one sending. So I would like to send with another update key another 5 values.

Do I have to use another array instead of PageAdd for example? The lenght is ok, but should it be empty before new sending? I am confused.
Or I have just another sprintf defined like:

sprintf(pageAdd,"/update?key=YYYYYYYYYYYYYY&field1=%i&field2=%i&field3=%i&field4=%i&field5=%i",temp5,temp6,temp7,temp8,temp9);

Thank you!

2

If you use sprintf() twice with the same buffer array then the second use will overwrite the first and add the null terminator at the appropriate place. For example

int bb1 = 12345;
int bb2 = 678;
char buffer[10];

void setup() 
{
  Serial.begin(115200);
  sprintf(buffer, ">%d<", bb1);
  Serial.println(buffer);

  sprintf(buffer, ">%d<", bb2);
  Serial.println(buffer);
}

void loop() 
{
}
3

That sound perfect in this case! Thanks for UKHeliBob helping again with sprintf !!!

4

As a general guide, I recommend using snprintf() rather than sprintf(), to protect you from overrunning the bounds of the array.