Just can't get 2 strings to join

Projects Programming
1

Hi all. Have been googling since last night and I just can't find the correct solution for this. I know it is a simple thing, but without C experience ( only VB ) I just don't understand why this seems to be so complicated.

Yes, I know the answers are out there, but I've been hunting for hours and just can't get this resolved. Please help.

The bottom line of what I am trying to do, is to pass a string to a function (void PRtxt) and have that function work with the passed string.
Final use would be to join strings for Serial.println, or for writing to an SD card, etc.

Questions:
Is it correct in the setup() to join strings using . & or + ?
Is it correct to pass the String to PRtxt, or does it first need to be converted to a char array ?
In the PRtxt function, can I join a char and a string ( String sLine = pTxt . " doesn't exist."; ) ?

void PRtxt(char pTxt[])
{
    String sLine = pTxt . " doesn't exist.";
    Serial.println(sLine);
}

void setup(void)
{
	Serial.begin(9600);
	Serial.print("Starting Sequence...");

    String aLine = "Test " . " text line 1";

	PRtxt(aLine);  

}
2

OK. Have just found sprintf. I think this may hold the solution.

Should the following work, or will I again get conflicts between the 'char' received by the 'MKfile' function and the String I want to join to it ?

#include <SD.h>
#include <stdio.h>

const int chipSelect = 4;

void MKfile(char fName[])
{
  char buffer [100];
  int n;

  if (SD.exists(fName)) {
    n=sprintf (buffer, "%s %s", fName, " exists");
    Serial.println(buffer);
  }
  else {
    n=sprintf (buffer, "WARNING : %s %s", fName, " does NOT exist");
    Serial.println(buffer);
  }

  // open a new file and immediately close it:
  File myFile;
  myFile = SD.open(fName, FILE_WRITE);
  myFile.close();

  // Check to see if the file exists: 
  if (SD.exists(fName)) {
    n=sprintf (buffer, "The file : %s %s", fName, " exists");
    Serial.println(buffer);
  }
  else {
    n=sprintf (buffer, "WARNING : The file : %s %s", fName, " does NOT exist.");
    Serial.println(buffer);
  }
}


void setup(void)
{
	Serial.begin(9600);
	Serial.print("Initializing SD card...");
	// make sure that the default chip select pin is set to output, even if you don't use it:
	pinMode(10, OUTPUT);

	// see if the card is present and can be initialized:
	if (!SD.begin(chipSelect)) {
		Serial.println("Card failed, or not present");
		return;        // don't do anything more:
	}
	Serial.println("card initialized.");

	MKfile("datalog.txt");  
}


void loop(void)
{ 
}
3 
if (SD.exists(fName)) {
    n=sprintf (buffer, "%s " exists", fName );
  }
  else {
    n=sprintf (buffer, "WARNING : %s does NOT exist", fName);
  }
  Serial.println(buffer);

Would be more natural, no?

4

Hi AWOL

Thanks, and Yes, I agree with you.

I am just trying to use this as an example to learn how to add different data types together.

The 'fName' is a 'char' ( as passed to the function ) whereas the other variable is a String.

So from your example, either your code or my code would work ? ( with yours being cleaner )

5

So from your example, either your code or my code would work ?

Yes, but...

sprintf adds a tremendous amount of code to your sketch. You can use multiple Serial.print() statements to output all the data, without the overhead of the sprintf function.

6

DaveO:
OK. Have just found sprintf. I think this may hold the solution.

  if (SD.exists(fName)) {

n=sprintf (buffer, "%s %s", fName, " exists");
    Serial.println(buffer);
  }
  else {
    n=sprintf (buffer, "WARNING : %s %s", fName, " does NOT exist");
    Serial.println(buffer);
  }

sprintf() will work, and your code will work - but the code you're dealing with is very straightforward, and you can avoid sprintf if you wish to rearrange the message a bit:

  Serial.print("Starting Sequence...");
  Serial.print(fName);
  if (SD.exists(fName)) 
    Serial.print(" exists");
  else
    Serial.print(" DOES NOT EXIST");

or even

  Serial.print("Starting Sequence...");
  Serial.print(fName);
  Serial.print(  SD.exists(fName)  ?  " exists"  : " DOES NOT EXIST"  );

for slightly shorter code