title: Arduino SD library directory naming rules
body: <p>I want to create some directories that represent dates, for example "11.03.24" but it seems like the SD.mkdir() function return false whenever I use special characters in my path. Strangely enough, the SD succeeds to make the directories that have only 1 special character in their naming like "@/fasdaf/".
  It is allowed to use special characters in the SD library?</p>
  
  <pre><code>void setup() {
  
    // Open serial communications and wait for port to open:
    Serial.begin(9600);
    while (!Serial) {
      ; // wait for serial port to connect. Needed for native USB port only
    }
  
  
    Serial.print("Initializing SD card...");
  
    if (!SD.begin(8)) {
      Serial.println("initialization failed!");
     return;
    }
    Serial.println("initialization done.");
  
  if(SD.mkdir("vdfa/3143#2123/fasfd")){ 
      Serial.println("Succesfully created directory");
      }
  if(SD.mkdir("!")){
      Serial.println("Succesfully created directory1");
      }
      if(SD.mkdir("@")){
      Serial.println("Succesfully created directory2");
      }
      if(SD.mkdir("#")){
      Serial.println("Succesfully created directory3");
      }
      if(SD.mkdir("$")){
      Serial.println("Succesfully created directory4");
      }
      if(SD.mkdir("%")){
      Serial.println("Succesfully created directory5");
      }
      if(SD.mkdir("^")){
      Serial.println("Succesfully created directory6");
      }
      if(SD.mkdir("&amp;")){
      Serial.println("Succesfully created directory7");
      }
      if(SD.mkdir("*")){
      Serial.println("Succesfully created directory8");
      }
  
    void loop(){
  
  }
  </code></pre>
  
  <p>I get "Succesfully created" for 1, 2, 3, 4, 5, and 7 but not on the first one were the code works without that special character included</p>