Failure to recognise an empty String within an if/else if statement

goalJJB · Apr 23, 2023

Hello,

I have two key functions: one to select and open a folder within an SDcard one to select play an audio file.

I have both of these within:

Code:

void loop() {

  buttonInit();
  updateIO();
  displayInit();

  

  if(directoryPath == "") // -> How can I get it say that this is false?
  {
    getFolder();
  }
  
  else if(filePath == "") // *= folderNames[4]* OR give it directoryPath == "Drums"? 
  {
    getFile();
  }

  else
  {
    homeScreen();
  } 
  
}

My aim is that once the directoryPath has been found, it should proceed to grab the filePath which can then be assigned to a pad. However, it always believes that no directory has been found and so never moves onto the else if statement. My specific question is, why does it always fail to see that a directoryPath has been found?

(Here is the whole of the code)

Code:

#include <SD.h>
#include <SPI.h>
#include <Bounce2.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <Audio.h>
#include <string>

#include "displayFunctions.h"

Adafruit_SSD1306 display(128, 64, &Wire, -1);

#define MOSI_PIN 11
#define SCK_PIN 13
#define CS_PIN = BUILTIN_SDCARD


void homeScreen();
void printDirectory(File dir, int numTabs);
void buttonInit();
void updateIO();
bool checkWav(String wav);

#define maxNumCharDisplay 80

int led = 28;

const char *folderNames[] = { "Drums", "Vocals", "Pads", "Misc" };

Bounce selectButton = Bounce(36, 10);
Bounce returnButton = Bounce(37, 10);


const byte pins[] = {28, 29, 30, 31, 32, 33, 34, 35};
const byte numOfPads = sizeof(pins);
Bounce padPad[numOfPads];

File root;
File currentDirectory;
File entry;

String dirArray;
String directoryPath;// = "/Presets/";
String filePath;  //-> copy this into ch array ?

bool selectedFolder;

int folderChoice;
int fileChoice;
int numTabs;

char presetFolderName[] = "/Presets/";
String fileExtension = ".wav";


int assignedPad = -1;

AudioPlaySdWav playWav;

void setup() {
  
  buttonInit();
  updateIO();
  displayInit();

  Serial.begin(9600);


 
  SPI.setMOSI(MOSI_PIN);
  SPI.setSCK(SCK_PIN);

  if (!(SD.begin(BUILTIN_SDCARD))) {
    while (1) {
      Serial.println("unable to access SD card.");
    }
  }

  homeScreen(); //  Display list of preset folders

  AudioMemory(8); //  buffer for how much memory to provide
  playWav.stop();

  
  
}


void loop() {

  buttonInit();
  updateIO();
  displayInit();

  
  //char presetFolderName[0];
  //sprintf(presetFolderName, '\0');

  //if(strlen(presetFolderName) > 0) // -> How can I get it say that this is false? -  && presetFolderName == '\0'
  if(directoryPath == "")
  {
    getFolder();
  }
  //else if(strlen(presetFolderName) < 0) // *= folderNames[4]* OR give it directoryPath == "Drums"?
  else if(filePath == "") 
  {
    getFile();
  }

  else
  {
    homeScreen();
  }


  
  
}

void getFolder()  //  this should return/input a String (folder name) -> Although, the folderNames are const chars? if a const char
{

  dirArray = directoryPath;
  //strcat(dirArray, PresetFolderName);         //  concatenate /Presets/ with directory path -> should this happen later?
  for (uint8_t i = 0; i < directoryPath.length(); i++)  //  for the whole length of the String
  { 
    //Serial.println("line 142"); 
    //Serial.println(dirArray[i]);                //   
  }
  
 
  if (directoryPath == "") {  //  if no directory has been selected 

    while (!selectButton.update()) {}

    if (selectButton.fallingEdge()) {
      //int folderChoice = readInt(1, 4); // -> do the same as^ by changing int into a ch Array

      //int folderChoice; //  keeps track of which folder has been selected -> should this be -1? -> could just say -1 here instead of further down
      char folderChoiceChar[maxNumCharDisplay + sizeof(char)];
      sprintf(folderChoiceChar, "%d", folderChoice);  //  But how do I get it to read from 1-4? -> for loop
      for (int i = 0; i < 3; i++) {
        folderChoice = folderChoiceChar[i];  //should the folderChoiceChar be tracked with an index? -> yes
      }

   
      dirArray = presetFolderName;
      
     
 
      dirArray += folderNames[folderChoice];

      File folder;
      folder = SD.open(dirArray.c_str());
           
     
      //folder = SD.open(directoryPath.c_str()); //  Does this open straight to ...^ "directoryPath = "/Presets + folderName;"

      
      if(folder.isDirectory()){  //  
       
    
        while (true) //Does this loop & print twice?
        {
          File entry = folder.openNextFile(); //  I think, because it's just 'openNextFile' whilst Drums is a directory -> it will keep looping on the drums directory until all files are printed. 
      

          if (!entry) 
          {
            break;
          }
          display.clearDisplay();
          display.setTextColor(SSD1306_WHITE);  // Draw white text
          display.setCursor(0, 0);
          
          Serial.println("---LOOP START---");
          display.println(folder.name()); //  this prints: e.g. "Drums" - How to print multiple??
          Serial.println(folder.name());
          display.setCursor(12, 0);
          display.println(":");          
          

         
          for(uint8_t i = 0; i < numTabs; i++)
          {
            
            display.println('\t');  //  This line should print vertically
            
          }
          display.println(entry.name());  //  And this prints the audio - but only 1 file - how can we print multiple?
          Serial.println(entry.name());

          if(entry.isDirectory()) //  This is if it is a folder not a file -> not necessary?
          {
            display.println("/");

          }
          else
          {
            Serial.println("");
          }
           
          entry.close();
          
          Serial.println("---LOOP END^--");

          break; // -> this work in only printing 1 audio file - now how multiple?

        }
        
        

        Serial.println(sizeof(directoryPath), DEC); //  prints the no. of bytes directoryPath takes up
        Serial.println(" bytes");
        
      }
      folder.close();
      display.display();
    
      
    }
     //WRITE OUT OF BOUNDS IF PRESETFOLDERNAME IS LONGER THAN 0 CHARS. - HOW?




   
  
  } 

 


}

void getFile()
{

  //char samplesArr[filePath.length() + 1];  //  change path from string to Char arry -> think the +1 is becuase of the NULL character at the end
  //strcpy(samplesArr, filePath.c_str());    //  copy String directoryPath into destination dirArray
  
  String samplesArr = filePath;
  
  
  for (uint8_t i = 0; i < filePath.length(); i++)  //  
  {                                                // 
   
  }

  if (filePath == "") //  if directory has been selected but no audio file, proceed. I think filePath has to be more defined before^
                            //  Currently just saying, if String filePath is nothing -> must make it so that filePath = charArray 
  {  

    while (!selectButton.update()) {}

    if (selectButton.fallingEdge() && checkWav(filePath)) //  -> AND if .wav?
    {


   
      char fileChoiceChar[maxNumCharDisplay + sizeof(char)];
      sprintf(fileChoiceChar, "%d", fileChoice);  //  But how do I get it to read from 1-4? -> for loop
      for (int i = 0; i < 3; i++) {
        fileChoice = fileChoiceChar[i];  //should the folderChoiceChar be tracked with an index? -> yes
      }

      samplesArr = dirArray; // -> ???

      samplesArr += dirArray[fileChoice];  //  -> what should I change folderNames to?

   
      

      display.clearDisplay();
      display.setCursor(0, 0);
      display.println("Assign to pad:");

      for (int i = 0; i < numOfPads; i++) {
        display.print(i + 1);
        display.print(". Pad ");
        display.print(i);
      }
      display.display();
    }
  } else if (assignedPad == -1) {                         // Definitley have to do some joining of assignedPad = filePath?
    for (int i = 0; i < numOfPads; i++) {
      if (padPad[i].update() && padPad[i].fallingEdge()) {
        assignedPad = -1;  // should this be -1?
        display.clearDisplay();
        display.setCursor(0, 0);
        display.print("Assigned to pad: ");
        display.println(assignedPad + 1);
        display.display();
      }
    }
  }

  else {
    for (int i = 0; i < numOfPads; i++) {
      if (padPad[i].update() && padPad[i].fallingEdge() && i == assignedPad) {
        playWav.play(filePath.c_str());
        break;
      }
    }
  }
 
  
}

void homeScreen()
{

  while (!returnButton.update()){}
  if(returnButton.fallingEdge())
  {
    
  
    display.clearDisplay();
    display.setCursor(0, 0);
    display.println("Select a directory:");
    for (int i = 0; i < 4; i++) {
      display.print(i + 1);
      display.print(". ");
      display.println(folderNames[i]);
    }
    display.display();
  }
}

void printDirectory(File dir, int numTabs) {

  while (true) {

    File entry =  dir.openNextFile();

    if (! entry) {

      // no more files

      break;

    }

    for (uint8_t i = 0; i < numTabs; i++) 
    {

      display.print('\t');

    }

    display.print(entry.name());

    if (entry.isDirectory()) 
    {

      display.println("/");

      printDirectory(entry, numTabs + 1);

    } else 
    {

    }
    entry.close();
  }
}

bool checkWav(String wav)
{
  if (wav.endsWith(fileExtension))
  {
    return true; // Return true if file ends with wav
  }
  else
  {
    return false; // Return false if file does not
  }
}

void displayInit() {
  display.begin(SSD1306_SWITCHCAPVCC, SCREEN_ADDRESS);
  display.clearDisplay();
  display.setTextSize(1);               // Normal 1:1 pixel scale
  display.setTextColor(SSD1306_WHITE);  // Draw white text
  display.setCursor(0, 0);
}

void buttonInit() {

  pinMode(36, INPUT_PULLUP);  // select button
  pinMode(37, INPUT_PULLUP);  // return button

  for(byte i = 0; i < numOfPads; i++)
  {
    padPad[i].attach(pins[i], INPUT_PULLUP);
    padPad[i].interval(5); //  debounce time    
  }


  pinMode(led, OUTPUT);
}

void updateIO()
{
  selectButton.update();
  returnButton.update();

  for(byte i = 0; i < numOfPads; i++)
  padPad[i].update();
   
}

I have tried stating (!(directoryPath == "")) as well as if directoryPath = one of the folderNames. as well as providing the void directoryPath(with a const char) to represent one of the folder names as this is what will be returned. I have also tried stating within void loop that if(strlen(presetFolderNames) > 0) { getFolder()}.

Uija · Apr 23, 2023

Cannot really see on my phone what string class you use, but stren is for char arrays that build a string. I’m am quite sure there are functions like empty() len() or size() on it.

KurtE · Apr 23, 2023

Sorry, I don't use Strings so unclear to me best way to use them here.

But you might try something like:
if (directoryPath.length() == 0)

or != 0 for other case...

I did not see anywhere where the directoryPath was assigned a value.

MichaelMC · Apr 23, 2023

Try "if (!*directoryPath)" or "if (directoryPath[0] == '\0')". But this won't really solve the bigger issue. Instead of testing for string completeness in the main loop(), instead, check for a raised flag that's been set elsewhere from where the string (path contents) originated.

goalJJB · Apr 23, 2023

New assigned value

KurtE said:
Sorry, I don't use Strings so unclear to me best way to use them here.

But you might try something like:
if (directoryPath.length() == 0)

or != 0 for other case...

I did not see anywhere where the directoryPath was assigned a value.

Yes, I realised this after posting, I therefore updated it so that directoryPath = dirArray; at the end of the getFolder() function.

Thank you for your suggestion. I have tried a number of methods stating that `if (directoryPath.length() == 0)` & `if(directoryPath[0] == '\0')`. But neither seem to progress to the getFile() function which should then print "assign to pad".

Even after I put Serial.println(directoryPath); after the `directoryPath = dirArray;` which outputs /Presets/Drums. This is the correct output and so proves that all of the attempted if statements above should be false but still it doesn't proceed. I can't see where I have gone wrong later in code?

Thanks

KurtE · Apr 23, 2023

Sorry hard to know what you have in there now.

In cases like this, I would put in some Serial.print(... like statements before each part like:

Code:

  Serial.println(directoryPath);
  Serial.println(directoryPath.length());
  Serial.println(filePath);
  ..
  if(directoryPath == "") // -> How can I get it say that this is false?
  {
    getFolder();
    Serial.println("getFolder Called");
  }
  
  else if(filePath == "") // *= folderNames[4]* OR give it directoryPath == "Drums"? 
  {
    getFile();
    Serial.println("getFile called");    
  }

  else
  {
    homeScreen();
    Serial.println("homeScreen called");
  } 
  
}

And see what the values are...

I don't know your needs here, but for example does filePath change if getFolder() is called if so you probably don't want the test under an else if....

goalJJB · Apr 23, 2023

Yes, when
if(directoryPath == "")
{
getFolder();
}

With the current code being:

Code:

void loop() {

  updateIO();
  displayInit();


  if(directoryPath.length() == 0) 
  {
    getFolder();
  }
  
  else
  {
    getFile();
  }
  

  while (!returnButton.update()){}
  if(returnButton.fallingEdge())
  {
    homeScreen();
  }
  
}

void getFolder()  //  this should return/input a String (folder name) -> Although, the folderNames are const chars? if a const char
{

  dirArray = directoryPath;
  

 
  for (uint8_t i = 0; i < directoryPath.length(); i++)  //  for the whole length of the String
  { 
    
  }


  if (directoryPath.length() == 0) {  //  if no directory has been selected 

    while (!selectButton.update()) {}

    if (selectButton.fallingEdge()) {
    
     
      char folderChoiceChar[maxNumCharDisplay + sizeof(char)];
      sprintf(folderChoiceChar, "%d", folderChoice);  //  But how do I get it to read from 1-4? -> for loop
      for (int i = 0; i < 3; i++) {
        folderChoice = folderChoiceChar[i];  //should the folderChoiceChar be tracked with an index? -> yes
      }

    
      dirArray = presetFolderName;
      
      String folderName = folderNames[folderChoice - 1];  //  does this actually do anything? -> could be used for proceeding
      

      dirArray += folderNames[folderChoice];

      File folder;
      folder = SD.open(dirArray.c_str());


      
      if(folder.isDirectory()){  //  
      

        while (true) //Does this loop & print twice?
        {
          File entry = folder.openNextFile(); //  I think, because it's just 'openNextFile' whilst Drums is a directory -> it will keep looping on the drums directory until all files are printed. 
         

          if (!entry) 
          {
            break;
          }
          display.clearDisplay();
          display.setTextColor(SSD1306_WHITE);  // Draw white text
          display.setCursor(0, 0);
          
        
          Serial.println("---LOOP START---");
          display.println(folder.name()); //  this prints: e.g. "Drums" - How to print multiple??
          Serial.println(folder.name());
          display.setCursor(12, 0);
          display.println(":");          
          
         
          for(uint8_t i = 0; i < numTabs; i++)
          {
           
            display.println('\t');  //  This line should print vertically
            
          }
          display.println(entry.name());  //  And this prints the audio - but only 1 file - how can we print multiple?
          Serial.println(entry.name());

          if(entry.isDirectory()) //  This is if it is a folder not a file -> not necessary?
          {
            display.println("/");

          }
          else
          {
            Serial.println("");
          }
           
          entry.close();
          
          Serial.println("---LOOP END^--");

          break; // -> this work in only printing 1 audio file - now how multiple?

        }
        
        
     
        
      }
            
      folder.close();
      display.display();
    
      
    }
   
  } 

    directoryPath = dirArray; // -> this output /Presets/Drums -> which is correct
    Serial.println(directoryPath);
    Serial.print("is ");
    Serial.print(directoryPath.length());
    Serial.print(" characters\n");
}

The output is:
Drums
DrumLoop1.wav
/Presets/Drums
is 14 characters

getFolder() should grab the folder which stores the audio files, the getFile() should grab a specific audio file which is stored in filePath. Which is then assigned to 1 of 8 pads, which can then play back the audio file.

What would you advise on if not an else if?

MarkT · Apr 23, 2023

If you don't follow the forum rule we don't know what type directoryPath was declared as.

If it's type is char *, then be aware that == is not a string comparison operator, its a pointer comparison operator. Use strlen() or strcmp(). There's no reason to suppose that "" == "", if they are represented in different parts of memory.

In general expect == to report if the representations are identical, not that the values represented are the same. In many situations the same value can have multiple representations, unless the value itself fits in a register. Sometimes == is overloaded to work for value equality, but you are at the mercy of the implementer of the class in question.

Failure to recognise an empty String within an if/else if statement

goalJJB

Member

Uija

Well-known member

KurtE

Senior Member+

MichaelMC

Well-known member

goalJJB

Member

KurtE

Senior Member+

goalJJB

Member

MarkT

Well-known member