#include <SD.h>
#include <SPI.h>

Sd2Card card;
SdVolume volume;
SdFile root;
File datafile;

String SD_card_reading(String path) {
  datafile = SD.open(path.c_str());
  String sd_data = "";
  while (datafile.available()) {
    sd_data = String(sd_data) + String(char(datafile.read()));
  }
  return sd_data;
}

void setup(){
  SD.begin(10);
  card.init(SPI_HALF_SPEED, 10);
  Serial.begin(9600);
  volume.init(card);
  Serial.println(card.type());
  Serial.println(String(volume.blocksPerCluster()*volume.clusterCount()/2/1024) + String("MB"));
  root.openRoot(volume);
  root.ls(LS_R | LS_DATE | LS_SIZE);
  if (SD.exists("fileName.txt")) {
    Serial.println(SD_card_reading("fileName.txt"));
  }
  datafile = SD.open("fileName.txt", FILE_WRITE);
  if(datafile){
   datafile.print("您好");
   datafile.println("");
   datafile.close();
  }
}

void loop(){
  //SD卡拥有超大的存储容量，一般用来保存检测传感器数据与系统参数
  //如温湿度数据等

}