Arduino 从 Txt 读取 Integer

Question

I'm trying to read my integer txt file from sd card.

My txt has these 2 lines (first line is 1, second is \n);

1

I did a reader code like;

#include <SD.h>
#include <SPI.h>
File myFile;
int pinCS = 53;
void setup() {
    
  Serial.begin(9600);
  pinMode(pinCS, OUTPUT);
  
  // SD Card Initialization
  if (SD.begin())
  {
    Serial.println("SD card is ready to use.");
  } else
  {
    Serial.println("SD card initialization failed");
    return;
  }
  // Reading the file
  myFile = SD.open("test.txt", FILE_READ);
  if (myFile) {
    Serial.println("Read:");
    // Reading the whole file
    while (myFile.available()) {
      Serial.write(myFile.read());
   }
    myFile.close();
  }
  else {
    Serial.println("error opening test.txt");
  }
  
}
void loop() {
  // empty
}

It works but what I want is read my integer from txt file and sum with another integer (that is int total in my below code. I tried this but it doesn't work;

#include <SD.h>
#include <SPI.h>
File myFile;
int pinCS = 53; // Pin 10 on Arduino Uno
int total = 3;
void setup() {
    
  Serial.begin(9600);
  pinMode(pinCS, OUTPUT);
  
  // SD Card Initialization
  if (SD.begin())
  {
    Serial.println("SD card is ready to use.");
  } else
  {
    Serial.println("SD card initialization failed");
    return;
  }
  // Reading the file
  myFile = SD.open("test.txt", FILE_READ);
  if (myFile) {
    Serial.println("Read:");
    // Reading the whole file
    while (myFile.available()) {
      total += myFile.read();
      Serial.write(total);
   }
    myFile.close();
  }
  else {
    Serial.println("error opening test.txt");
  }
  
}
void loop() {
  // empty
}

What am I missing? Can you fix my code?

Answer 1

read() reads one character, so you have to convert the sequences of characters to integer value.

    while (myFile.available()) {
      total += myFile.read();
      Serial.write(total);
   }

should be

    int current = 0;
    while (myFile.available()) {
      int c = myFile.read();
      if ('0' <= c && c <= '9') {
        current = current * 10 + (c - '0');
      } else if (c == '\n') {
        total += current;
        current = 0;
        Serial.write(total);
      }
    }