c++ - 为什么我的 if 子句不起作用？如何修复变量类型？

Question

我想用udp语句改参数。我正在获取 udp，但我的 if 子句不起作用。怎么能 comper 2个变量？

我更改了变量类型和/或 if 子句类型(例如 if ( strcmp ( UdpMsg , "relay01_off") == 0) )。

设置IF子句变量

String UdpMsg = "12345";...

获取UDP报文

String UdpMsg ((char *)buffer);...

IF 子句

if ( UdpMsg == "relay01_off" ) {
  digitalWrite(relay_pin, HIGH);
  Serial.print ("You!\n");
  }

我期待看到“你!”当我发送 UDP 但它找不到相等时。

信息的完整代码:

#include <WiFi.h>
#include <WiFiUdp.h>
#include <cstring>  //For the string functions

const char* wifi_name = "SSID";          // Your Wifi network name here
const char* wifi_pass = "password";     // Your Wifi network password here
WiFiServer server(80);                      // Server will be at port 80

// IP address to send UDP data to.
const char *  udpAddress = "192.168.1.6";
int           udpPort = 4444;

//create UDP instance
WiFiUDP udp;

// relay PINi
int relay_pin = 15;

// UDP Mesajı gelen
String UdpMsg = "12345";

void setup() 
{
  Serial.begin (115200);
  pinMode (relay_pin, OUTPUT);

  Serial.print ("Connecting to ");
  Serial.print (wifi_name);
  WiFi.begin (wifi_name, wifi_pass);     // Connecting to the wifi network

  while (WiFi.status() != WL_CONNECTED) // Waiting for the response of wifi network
  {
    delay (500);
    Serial.print (".");
  }
  Serial.println("");
  Serial.println("Connection Successful");
  Serial.print("IP address: ");
  Serial.println(WiFi.localIP());           // Getting the IP address
  Serial.println("Type the above IP address into browser search bar"); 
  server.begin();                           // Starting the server
  digitalWrite(relay_pin, LOW);           // switch i AC

  //This initializes udp and transfer buffer
  udp.begin(udpPort);
}

void loop() 
{
  uint8_t buffer[50] = "";
  //processing incoming packet, must be called before reading the buffer
  udp.parsePacket();
  //receive response from server, it will be HELLO WORLD
  if(udp.read(buffer, 50) > 0){
    Serial.print("Recevied UDP: ");
    Serial.println((char *)buffer);
    String UdpMsg ((char *)buffer);
  }

  //////// UDP IF leri ///////////
  if ( UdpMsg == "relay01_off" ) {        // Equal strings
    digitalWrite(relay_pin, HIGH);
    Serial.print ("You!\n");
  }

}

Answer 1

您似乎在以下位置构建了第二个 UdpMsg 变量:

  if(udp.read(buffer, 50) > 0){
    Serial.print("Recevied UDP: ");
    Serial.println((char *)buffer);
    String UdpMsg ((char *)buffer); // <--- 2nd UdpMsg, released after 'if' clause
  }

当 UdpMsg 在这一行时:

if ( UdpMsg == "relay01_off" )

指第一个，全局的，保持初始值“12345”。