How to use the SD folder's name here?

[shanren]

Hi all.
I'd like to operate the SD with subfolder, if set: String stringA = "Friday"; write a file into subfolder 'Friday', failed, how to fix please?

tested: 'writeFile(SD, "/Friday/Mondayhello.txt", "mmHello ");` works fine.

Thanks
Adam

#include "FS.h"
#include "SD.h"
#include "SPI.h"

String stringA = "Friday";
String stringB = "Wednesday";
String stringC;

String StrWK[7] = {"Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"};

int writeFileButtonmark = 1;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);

  SDsetup();

  if (writeFileButtonmark == 1) {

    for (int i = 0; i < 7; i++) {
      if (stringA == StrWK[i]) {
        Serial.print("L36strArray["); Serial.print( i); Serial.print( "] =");
        Serial.println(StrWK[i]);

        writeFile(SD, "/StrWK[i]/Mondayhello.txt", "mmHello ");
        appendFile(SD, "/StrWK[i]/Mondayhello.txt", "mmWorld!\n");
        readFile(SD, "/StrWK[i]/Mondayhello.txt");
        writeFileButtonmark = 0;
        delay(1000);
      }
    }
  }
}

void loop() {
  // put your main code here, to run repeatedly:

}


void readFile(fs::FS & fs, const char * path) {
  Serial.printf("Reading file: %s\n", path);

  File file = fs.open(path);
  if (!file) {
    Serial.println("Failed to open file for reading");
    return;
  }

  Serial.print("Read from file: ");
  while (file.available()) {
    Serial.write(file.read());
  }
  file.close();
}

void writeFile(fs::FS & fs, const char * path, const char * message) {
  Serial.printf("Writing file: %s\n", path);

  File file = fs.open(path, FILE_WRITE);
  if (!file) {
    Serial.println("Failed to open file for writing");
    return;
  }
  if (file.print(message)) {
    Serial.println("File written");
  } else {
    Serial.println("Write failed");
  }
  file.close();
}

void appendFile(fs::FS & fs, const char * path, const char * message) {
  Serial.printf("Appending to file: %s\n", path);

  File file = fs.open(path, FILE_APPEND);
  if (!file) {
    Serial.println("Failed to open file for appending");
    return;
  }
  if (file.print(message)) {
    Serial.println("Message appended");
  } else {
    Serial.println("Append failed");
  }
  file.close();
}


void SDsetup() {
  Serial.begin(115200);
  if (!SD.begin()) {
    Serial.println("Card Mount Failed");
    return;
  }
  uint8_t cardType = SD.cardType();

  if (cardType == CARD_NONE) {
    Serial.println("No SD card attached");
    return;
  }

  Serial.print("SD Card Type: ");
  if (cardType == CARD_MMC) {
    Serial.println("MMC");
  } else if (cardType == CARD_SD) {
    Serial.println("SDSC");
  } else if (cardType == CARD_SDHC) {
    Serial.println("SDHC");
  } else {
    Serial.println("UNKNOWN");
  }

  uint64_t cardSize = SD.cardSize() / (1024 * 1024);
  Serial.printf("SD Card Size: %lluMB\n", cardSize);

}

OUTPUT:

D Card Type: SDHC
SD Card Size: 29818MB
L36strArray[4] =Friday
Writing file: /StrWK[i]/Mondayhello.txt
Failed to open file for writing
Appending to file: /StrWK[i]/Mondayhello.txt
Failed to open file for appending
Reading file: /StrWK[i]/Mondayhello.txt
Failed to open file for reading

[van_der_decken]

You need to investigate the sprintf function.

And no doubt someone will be along shortly to tell you not to use Strings, for perfectly valid reasons.

[shanren]

Thank you.
It works.