String startsWith and endsWith Functions —— Arduino Documentation

String startsWith and endsWith Functions —— Arduino Documentation

用法

startsWith(string, int) 是可以带位置参数的，那就是可以在任何地方找字符串了

stringOne = "HTTP/1.1 200 OK";
if (stringOne.startsWith("200 OK", 9)) {
Serial.println("Got an OK from the server");
}

等同于下面 substring() 的写法

stringOne = "HTTP/1.1 200 OK";
if (stringOne.substring(9) == "200 OK") {
Serial.println("Got an OK from the server");
}

用 substring() 时，是默认到结束吗？ 不是的，详见：

String substring Function | Arduino Documentation

例：http报文解析

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
  }
}

void loop() {
  // startsWith() checks to see if a String starts with a particular substring:
  String stringOne = "HTTP/1.1 200 OK";
  Serial.println(stringOne);
  if (stringOne.startsWith("HTTP/1.1")) {
    Serial.println("Server's using http version 1.1");
  }

  // you can also look for startsWith() at an offset position in the string:
  stringOne = "HTTP/1.1 200 OK";
  if (stringOne.startsWith("200 OK", 9)) {
    Serial.println("Got an OK from the server");
  }

  // endsWith() checks to see if a String ends with a particular character:
  String sensorReading = "sensor = ";
  sensorReading += analogRead(A0);
  Serial.print(sensorReading);
  if (sensorReading.endsWith("0")) {
    Serial.println(". This reading is divisible by ten");
  } else {
    Serial.println(". This reading is not divisible by ten");
  }

  // do nothing while true:
  while (true);
}