part of code appended into string, resulting in very strange serial output

Projects General Guidance
1

Hi, i am getting very strange serial output for my arduino project

the following code

Serial.print("curr[b]entChar:[/b]");Serial.println(currentChar);
printChar(currentChar);

void printchar(char currentChar){
    String charFilename = currentChar + ".tmp";
    Serial.print("charFilename: ");Serial.println(charFilename);
    
    String filepath = customTextPath + charFilename;
    Serial.print("fp:");Serial.println(filepath);
 
     filepath.toCharArray(infile, 20); 
     
     Serial.print("printChar: infile:");Serial.println(infile);
}

results in the following on serial monitor

currentChar:A
charFilename: [b]entChar:[/b]
fp:characters/entChar:
printChar: infile:characters/entChar:

why is part of the code appended into the string???

Sketch uses 36622 bytes (28%) of program storage space. Maximum is 130048 bytes.
Global variables use 2610 bytes (31%) of dynamic memory, leaving 5582 bytes for local variables. Maximum is 8192 bytes.

this the results of uploading on arduino IDE

2

That's not a program. Please read How to Use the Forum.

3

-dev:
That's not a program. Please read How to Use the Forum.

perhaps ive used the wrong word.

I am having strange serial output for my arduino project..

4

tzijie:
perhaps ive used the wrong word.

The word you're looking for is "snippet".

We hate snippets

5

Please post the complete program. The problem is usually in the part we can't see and in which you are probably not looking.

It is not a good idea to use the String (capital S) class on an Arduino as it can cause memory corruption in the small memory on an Arduino. Just use cstrings - char arrays terminated with 0.

...R

6

I think this line is part of your problem:

  String charFilename = currentChar + ".tmp";

Since your printout shows currentChar == 'A' I think you are getting:

  String charFilename = &".tmp"+65;

Since ".tmp" is only 5 bytes long and you are starting at the 66th byte I expect you will get something unexpected.

You can't concatenate a character and a character string. Try this instead:

  String charFilename = currentChar;
charFilename += ".tmp";

I'm not sure that is the only mistake since many of the variable are not declared.

7

johnwasser:
I think this line is part of your problem:

  String charFilename = currentChar + ".tmp";

Since your printout shows currentChar == 'A' I think you are getting:

  String charFilename = &".tmp"+65;

Since ".tmp" is only 5 bytes long and you are starting at the 66th byte I expect you will get something unexpected.

You can't concatenate a character and a character string. Try this instead:

  String charFilename = currentChar;

charFilename += ".tmp";






I'm not sure that is the only mistake since many of the variable are not declared.

Thank you! i realise strings in arduino and andriod are a little different. and did the concat one at a time. its working now.

String tmpFilename = customTextPath + font;
		tmpFilename += "/";
		tmpFilename += currentChar;
		tmpFilename += ".tmp";
		Serial.print(F("tmpFilename: "));Serial.println(tmpFilename);
		
		tmpFilename.toCharArray(infile, 20); 
		Serial.print("printChar: infile:");Serial.println(infile);