How can i get rid of the error "cannot convert 'String' to 'const char*'"

Question

I want to get this code to recognise different commands and be able to parse the rest of the command, fore example I send "/sleep 5", and it will sleep for 5 seconds. However, I keep on getting this error "cannot convert 'String' to 'const char*'". here is my code:

#define maxCommandLength 64
String commands[] = {"/test", "/say", "/reset", "/sleep"};
void setup() {
 // put your setup code here, to run once:
 Serial.begin(115200);
 Serial.println("Power on.");
}
char serial[maxCommandLength];
boolean valid;
void loop() {
 // put your main code here, to run repeatedly:
 Serial.println("Clearing command buffer(char 'serial'");
 for (byte i = 0; i < maxCommandLength; i++) {//if maxCommandLength is larger that 255, change 'byte i' to 'int i'
 serial[i] = ' ';
 }
 if (Serial.available()) {
 Serial.readBytesUntil(' ', serial, maxCommandLength);
 }
 if (serial[0] == '/') { //if it is a command
 Serial.print("Command recieved. \nCommand class:");
 Serial.println(serial);
 //test if command is valid
 for (byte i = 0; i < maxCommandLength; i++) {//if maxCommandLength is larger that 255, change 'byte i' to 'int i'
 valid = strcmp(serial,commands[i]);
 if(valid){
 break;
 }
 }
 //execution of command
 Serial.readBytesUntil(' ', serial, maxCommandLength);
 //.......
 }
}

Answer 1

there is no reason for command to be a String array. Instead make it a const char**:

const char** commands = {"/test", "/say", "/reset", "/sleep"};

• user35284: I found that yours wouldn't compile, but this would: const char* commands[] = {"/test", "/say", "/reset", "/sleep"};
• Nick Gammon: @RowanRadosav-McRae If this answers your question please accept the answer.

Answer 2

You can call the .c_str() method of String class returning (temporary) const char * representation of underlying string, in your case:

valid = strcmp(serial,commands[i].c_str());
// ^^^^^^^^ 

should work. Just make sure you don't keep the returned const char * around longer than necessary because by spec it is no guaranteed to remain valid.