I want to print error in case the word that i entered in the serial monitor is different from 9 of lenght but it prints error all the time because the program itself doenst know when i´m entering a word.
// C++ code
//
void setup()
{
Serial.begin(9600);
Serial.println("Checksum");
}
void loop()
{
String s = Serial.readString();
if (s.length() == 9)
{
for (int i = 0; i < 9; i++)
{
Serial.print(s[i]);
Serial.println(" ");
Serial.print((byte)s[i], HEX);
Serial.println(" ");
Serial.println(" ");
Serial.println();
}
Serial.println("Ok");
}
if (s.length() != 9)
{
//Serial.println("Error"); //here is the error
}
}
You only want handle the input if the user entered something. To test if there are some incoming characters, test Serial.available() before Serial.readString().
readString waits for the next character until timeout. Default timeout is 1000 milliseconds. So if you send a string from Serial Monitor, the readString function will wait one second after the last received character. You want to set a shorter timeout since the time between the received characters is in microseconds range. For example use Serial.setTimeout(10); to set the timeout to 10 milliseconds.
As an alternative to readString you can use readStringUntil or if you want to read into a characters buffer, then readBytesUntil.
If you have in Serial Monitor the line endings setting set to something else than 'no new line characters", then the received String will end with one or two new line characters which will make it longer then you expect. To remove these white space characters and any spaces around the entered text, you van use trim function of String as s.trim();
Related
Ive incorporated multiple features i want in a microcontroller program (ESP32 Wroom32) and needed some advice on the best way to keep the program running and receive messages while it is running.
Current code:
//includes and declarations
setup()
{
//setup up wifi, server
}
main(){
WiFiClient client = server.available();
byte new_command[40];
if (client) // If client object is created, a connection is setup
{
Serial.println("New wifi Client.");
String currentLine = ""; //Used to print messages
while (client.connected())
{
recv_byte = client.read();
new_command = read_incoming(&recv_byte, client); //Returns received command and check for format. If invalid, returns a 0 array
if (new_command[0] != 0) //Checks if message is not zero, None of valid messages start with zero
{
execute_command(new_command);
//new_command is set to zero
}
}//end of while loop
}//end of if loop
}
The downside of this is that the ESP32 waits till the command is finished executing before it is ready to receive a new message. It is desired that the ESP32 receive commands and store them, and execute it at its own pace. I am planning to change the current code to receive a messages while the code is running as follows:
main()
{
WiFiClient client = server.available();
byte new_command[40];
int command_count = 0;
byte command_array[50][40];
if (command_count != 0)
{
execute_command(command_array[0]);
//Decrement command_count
//Shift all commands in command_array by 1 row above
//Set last executed command to zero
}
}//end of main loop
def message_interrupt(int recv_byte, WiFiClient& running_client)
{
If (running_client.connected())
{
recv_byte = running_client.read();
new_command = read_incoming(&recv_byte, running_client); //Returns received command and check for format. If invalid, returns a 0 array
//add new command to command_array after last command
//increment command_count
}
}
Which interrupt do I use to receive the message and update the command_array ? https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-guides/wifi.html Doesnt mention any receive/transmit events. I couldnt find any receive/transmit interrupt either or maybe I searched for the wrong term.
Is there an efficient way to read the last line of a text file? Right now i'm simply reading each line with code like below. Then S holds the last line read. Is there a good way to grab that last line without looping through entire text file?
TStreamReader* Reader;
Reader = new TStreamReader(myfile);
while (!Reader->EndOfStream)
{
String S = Reader->ReadLine();
}
Exactly as Remy Lebeau commented:
Use file access functions FileOpen,FileSeek,FileRead
look here for example of usage:
Convert the Linux open, read, write, close functions to work on Windows
load your file by chunks from end into memory
so make a static buffer and load file into it from end by chunks ...
stop on eol (end of line) usually CR,LF
just scan for 13,10 ASCII codes or their combinations from end of chunk. Beware some files have last line also terminated so you should skip that the first time ...
known eols are:
13
10
13,10
10,13
construct line
if no eol found add whole chunk to string, if found add just the part after it ...
Here small example:
int hnd,siz,i,n;
const int bufsz=256; // buffer size
char buf[bufsz+1];
AnsiString lin; // last line output
buf[bufsz]=0; // string terminator
hnd=FileOpen("in.txt",fmOpenRead); // open file
siz=FileSeek(hnd,0,2); // obtain size and point to its end
for (i=-1,lin="";siz;)
{
n=bufsz; // n = chunk size to load
if (n>siz) n=siz; siz-=n;
FileSeek(hnd,siz,0); // point to its location (from start)
FileRead(hnd,buf,n); // load it to buf[]
if (i<0) // first time pass (skip last eol)
{
i=n-1; if (i>0) if ((buf[i]==10)||(buf[i]==13)) n--;
i--; if (i>0) if ((buf[i]==10)||(buf[i]==13)) if (buf[i]!=buf[i+1]) n--;
}
for (i=n-1;i>=0;i--) // scan for eol (CR,LF)
if ((buf[i]==10)||(buf[i]==13))
{ siz=0; break; } i++; // i points to start of line and siz is zero so no chunks are readed after...
lin=AnsiString(buf+i)+lin; // add new chunk to line
}
FileClose(hnd); // close file
// here lin is your last line
Windows 10 with latest updates installed on a Dell XPS13. US keyboard layout and US locale selected (not international). Still a call to kbhit() or _kbhit() with specific characters such as ", ~, % does not return the key hit, at least mot until a certain amount of time (~1second) and a second character has been hit.
I try to use kbhit() because I need a non-waiting function. How can I detect correctly a keyboard hit on " or % with a single keystroke?
In Linux using a timed-out select() on stdin works great, but doesn't seem to be OK with Windows.
Thanks,
-Patrick
I finally found a solution that fits my needs and fixes the issues I have with kbhit(); code below; I hope it helps others too.
– Patrick
int getkey();
//
// int getkey(): returns the typed character at keyboard or NO_CHAR if no keyboard key was pressed.
// This is done in non-blocking mode; i.e. NO_CHAR is returned if no keyboard event is read from the
// console event queue.
// This works a lot better for me than the standard call to kbhit() which is generally used as kbhit()
// keeps some characters such as ", `, %, and tries to deal with them before returning them. Not easy
// the to follow-up what's really been typed in.
//
int getkey() {
INPUT_RECORD buf; // interested in bKeyDown event
DWORD len; // seem necessary
int ch;
ch = NO_CHAR; // default return value;
PeekConsoleInput(GetStdHandle(STD_INPUT_HANDLE), &buf, 1, &len);
if (len > 0) {
if (buf.EventType == KEY_EVENT && buf.Event.KeyEvent.bKeyDown) {
ch = _getche(); // set ch to input char only under right conditions
} // _getche() returns char and echoes it to console out
FlushConsoleInputBuffer(GetStdHandle(STD_INPUT_HANDLE)); // remove consumed events
} else {
Sleep(5); // avoids too High a CPU usage when no input
}
return ch;
}
It is also possible to call ReadConsoleInput(GetStdHandle(STD_INPUT_HANDLE), &buf, 1, &len); rather than FlushConsoleInputBuffer(GetStdHandle(STD_INPUT_HANDLE)); in the code above, but for some unknown reason, it doesn't seem to reply/react as quickly and some character are missed when typing at the keyboard.
I found this code below on the internet which is suppose to count the sentences on an 8051 MCU.
Can someone please explain to me what is exactly happening where there are question marks.
Any kind of help would be highly appreciated.
#include<string.h>
char code *text=" what is a program? that has, a a lot of errors! When " ;
char code *text1=" you compile. this file, uVision. reports a number of? ";
char code *text2=" problems that you! may interactively correct. " ; //Null characters are also included in array!!!
void count ( char pdata* , char pdata*);
void main (void){
char pdata Nw,Ns;
char data TextNw[2],TextNs[2];
count(&Nw, &Ns); // call subroutine
TextNw[0]=Nw/10; //?????????????????????????????????
TextNw[1]=Nw%10; //?????????????????????????????????
TextNs[0]=Ns/10; //?????????????????????????????????
TextNs[1]=Ns%10; //?????????????????????????????????
while(1);
}
void count ( char pdata *Nw, char pdata *Ns ){
unsigned char N, i, ch;
typedef enum {idle1, idle2} state; //?????????????????????????????????
state S; // begining state
P2=0x00; // pdata bank definition it must be performed first!!
*Ns=*Nw=0; // without proper start-up there is no initialisation, initialise now!!
S=idle1; // beginning state
N=strlen(text)+strlen(text1)+strlen(text2)+3; //????????????? + 3 to acount 3 Null characters!
P2=0x00; // pdata bank definition
for(i=0;i!=N;i++){
ch=text[i]; // take a caharacter from the text
switch (S)
{
case (idle1):{
if (ch==0) break; // skip NULL terminating character!
if (ch!=' '){
S=idle2;
(*Nw)++;
}
break;
}
case(idle2):{
if (ch==0) break; // skip NULL terminating character!
if((ch==' ')||(ch==','))S=idle1;
else if ((ch=='?')||(ch=='.')||(ch=='!')){
S=idle1;
(*Ns)++;
}
break;
}
}
}
}
This program does 2 things in conjunction - counts number of sentences in the text and counts the number of words in the text. Once the counting is done, the results are stored in 2-char arrays. For example, for 57 words in 3 sentences the results will be stored as this: TextNw = {'5','7'} and TextNs = {'0','3'}.
The variable N contains the full length of the text with the addition of 3 null terminating characters (one per sentence).
The algorithm simultaneously counts words and sentences. In idle1 state the counting is in word-counting mode. In idle2 state the counting is in sentence-counting mode. The modes are interchanged according to current character being read - if delimiter is encountered, the appropriate counter is increased.
I am trying to write a custom reader which serves me the purpose of reading a record (residing in two lines) with defined number of fields.
For Eg
1,2,3,4("," can be there or not)
,5,6,7,8
My requirement is to read the record and push it into mapper as a single record like {1,2,3,4,5,6,7,8}. Please give some inputs.
UPDATE:
public boolean nextKeyValue() throws IOException, InterruptedException {
if(key == null) {
key = new LongWritable();
}
//Current offset is the key
key.set(pos);
if(value == null) {
value = new Text();
}
int newSize = 0;
int numFields = 0;
Text temp = new Text();
boolean firstRead = true;
while(numFields < reqFields) {
while(pos < end) {
//Read up to the '\n' character and store it in 'temp'
newSize = in.readLine( temp,
maxLineLength,
Math.max((int) Math.min(Integer.MAX_VALUE, end - pos),
maxLineLength));
//If 0 bytes were read, then we are at the end of the split
if(newSize == 0) {
break;
}
//Otherwise update 'pos' with the number of bytes read
pos += newSize;
//If the line is not too long, check number of fields
if(newSize < maxLineLength) {
break;
}
//Line too long, try again
LOG.info("Skipped line of size " + newSize + " at pos " +
(pos - newSize));
}
//Exit, since we're at the end of split
if(newSize == 0) {
break;
}
else {
String record = temp.toString();
StringTokenizer fields = new StringTokenizer(record,"|");
numFields += fields.countTokens();
//Reset 'value' if this is the first append
if(firstRead) {
value = new Text();
firstRead = false;
}
if(numFields != reqFields) {
value.append(temp.getBytes(), 0, temp.getLength());
}
else {
value.append(temp.getBytes(), 0, temp.getLength());
}
}
}
if(newSize == 0) {
key = null;
value = null;
return false;
}
else {
return true;
}
}
}
This is the nextKeyValue method which I am trying to work on. But still the mapper are not getting proper values.
reqFields is 4.
Look at how TextInputFormat is implemented. Look at it's superclass, FileInputFormat as well. You must subclass Either TextInputFormat of FileInputFormat and implement your own record handling.
Thing to be aware when implementing any kind of file input format is this:
Framework will split the file and give you the start offset and byte length of the piece of the file you have to read. It may very well happen that it splits the file right across some record. That is why your reader must skip the bytes of the record at the beginning of the split if that record is not fully contained in the split, as well as read past the last byte of the split to read the whole last record if that one is not fully contained in the split.
For example, TextInoutFormat treats \n characters as record delimiters so when it gets the split it skips the bytes until the first \n character and read past the end of the split until the \n character.
As for the code example:
You need to ask yourself the following question: Say you open the file, seek to a random position and start reading forward. How do you detect the start of the record? I don't see anything in your code that deals with that, and without it, you cannot write a good input format, because you don't know what are the record boundaries.
Now it is still possible to make the input format read the whole file end to end by making the isSplittable(JobContext,Path) method return false. That makes the file read wholly by single map task which reduces parallelism.
Your inner while loop seems problematic since it's checking for lines that are too long and is skipping them. Given that your records are written using multiple lines, it can happen that you merge one part of one record and another part of another record when you read it.
The string had to be tokenized using StringTokenizer and not split. The code has been updated with the new implmentation.