help with char *

[f-peri]

I apologize in advance as this question is more a result of my lack of experience with pointers rather than your implementation. I also understand it's been some time since you've published this work. Thanks for putting together a great routine. When I run this sketch:

#include <CircularBuffer.h>

CircularBuffer<char*, 4> buffer;

void printBuffer() {
  if (buffer.isEmpty()) {
    Serial.println("empty");
  } else {
    Serial.println("[");
    for (decltype(buffer)::index_t i = 0; i < buffer.size(); i++) {
      Serial.println(buffer[i]);
    }
    Serial.println("]");

    Serial.print("(");
    Serial.print(buffer.size());
    Serial.print("/");
    Serial.print(buffer.size() + buffer.available());
    if (buffer.isFull()) {
      Serial.print(" full");
    }

    Serial.println(")");
  }
}

void setup() {
  Serial.begin(115200);
  while (!Serial)
    delay(100);

  char dataMessage[250] = "";

  strcpy(dataMessage,"1 is first in (oldest)");
  buffer.unshift(dataMessage);
  Serial.print("buffer is ");
  printBuffer();

  strcpy(dataMessage, "2 is second in");
  //Serial.printf("dataMessage second = %s\n", dataMessage);
  buffer.unshift(dataMessage);
  Serial.print("buffer is ");
  printBuffer();

  strcpy(dataMessage, "3 is middle");
  buffer.unshift(dataMessage);
  Serial.print("buffer is ");
  printBuffer();

  strcpy(dataMessage, "4 is next to newest");
  buffer.unshift(dataMessage);
  Serial.print("buffer is ");
  printBuffer();

  strcpy(dataMessage, "5 is newest");
  buffer.unshift(dataMessage);
  Serial.print("buffer is ");
  printBuffer();
}

void loop() {}

The result I get is:

buffer is [
1 is first in (oldest)
]
(1/4)
buffer is [
2 is second in
2 is second in
]
(2/4)
buffer is [
3 is middle
3 is middle
3 is middle
]
(3/4)
buffer is [
4 is next to newest
4 is next to newest
4 is next to newest
4 is next to newest
]
(4/4 full)
buffer is [
5 is newest
5 is newest
5 is newest
5 is newest
]
(4/4 full)

In my application the variable dataMessage is reused in loop(), but I've simplified here to demonstrate my question. I have run the experiment with multiple defined char arrays with success, however, when run as above, well you see the results.

Thanks for your help,
Frank

[rlogiacco]

What would be the expected output? Il giorno sab 28 ott 2023 alle 01:41 f-peri ***@***.***> ha scritto:

…

I apologize in advance as this question is more a result of my lack of experience with pointers rather than your implementation. I also understand it's been some time since you've published this work. Thanks for putting together a great routine. When I run this sketch: #include <CircularBuffer.h> CircularBuffer<char*, 4> buffer; void printBuffer() { if (buffer.isEmpty()) { Serial.println("empty"); } else { Serial.println("["); for (decltype(buffer)::index_t i = 0; i < buffer.size(); i++) { Serial.println(buffer[i]); } Serial.println("]"); Serial.print("("); Serial.print(buffer.size()); Serial.print("/"); Serial.print(buffer.size() + buffer.available()); if (buffer.isFull()) { Serial.print(" full"); } Serial.println(")"); } } void setup() { Serial.begin(115200); while (!Serial) delay(100); char dataMessage[] = "1 is first in (oldest)"; buffer.unshift(dataMessage); Serial.print("buffer is "); printBuffer(); strcpy(dataMessage, "2 is second in"); //Serial.printf("dataMessage second = %s\n", dataMessage); buffer.unshift(dataMessage); Serial.print("buffer is "); printBuffer(); strcpy(dataMessage, "3 is middle"); buffer.unshift(dataMessage); Serial.print("buffer is "); printBuffer(); strcpy(dataMessage, "4 is next to newest"); buffer.unshift(dataMessage); Serial.print("buffer is "); printBuffer(); strcpy(dataMessage, "5 is newest"); buffer.unshift(dataMessage); Serial.print("buffer is "); printBuffer(); } void loop() {} The result I get is: buffer is [ 1 is first in (oldest) ] (1/4) buffer is [ 2 is second in 2 is second in ] (2/4) buffer is [ 3 is middle 3 is middle 3 is middle ] (3/4) buffer is [ 4 is next to newest 4 is next to newest 4 is next to newest 4 is next to newest ] (4/4 full) buffer is [ 5 is newest 5 is newest 5 is newest 5 is newest ] (4/4 full) In my application the variable dataMessage is reused in loop(), but I've simplified here to demonstrate my question. I have run the experiment with multiple defined char arrays with success, however, when run as above, well you see the results. Thanks for your help, Frank — Reply to this email directly, view it on GitHub <#82>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AABQWMMIXAGWCF2OD3ERX6TYBRBELAVCNFSM6AAAAAA6TP2CMCVHI2DSMVQWIX3LMV43ERDJONRXK43TNFXW4OZVG44DKNZSGQ> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[f-peri]

Thanks for your prompt reply. My desire is to reuse the variable dataMessage. If I rewrite the code to use separate char *, as such:

CircularBuffer<char*, 4> buffer;

void printBuffer() {
  Serial.print("buffer is ");
  if (buffer.isEmpty()) {
    Serial.println("empty");
  } else {
    Serial.println("[");
    // for (decltype(buffer)::index_t i = 0; i < buffer.size(); i++) {
    for (int i = 0; i < buffer.size(); i++) {
      Serial.println(buffer[i]);
    }
    Serial.println("]");

    Serial.print("(");
    Serial.print(buffer.size());
    Serial.print("/");
    Serial.print(buffer.size() + buffer.available());
    if (buffer.isFull()) {
      Serial.print(" full");
    }

    Serial.println(")");
  }
}

void setup() {
  Serial.begin(115200);
  while (!Serial)
    delay(100);

  char dataMessage1[250] = "1";
  char dataMessage2[250] = "2";
  char dataMessage3[250] = "3";
  char dataMessage4[250] = "4";
  char dataMessage5[250] = "5";

  buffer.unshift(dataMessage1);
  printBuffer();

  buffer.unshift(dataMessage2);
  printBuffer();

  buffer.unshift(dataMessage3);
  printBuffer();

  buffer.unshift(dataMessage4);
  printBuffer();

  buffer.unshift(dataMessage5);
  printBuffer();
}

void loop() {}

then the output is:

buffer is [
1
]
(1/4)
buffer is [
2
1
]
(2/4)
buffer is [
3
2
1
]
(3/4)
buffer is [
4
3
2
1
]
(4/4 full)
buffer is [
5
4
3
2
]
(4/4 full)

which is the output I expected. I am fairly certain I am missing something quite obvious and thank you for your help.

[rlogiacco]

You can re-use the variable name, but you must assign a new memory space each time and you also have to take care of releasing such memory space. Have a look at the example where objects are stored in the buffer. In practice you need to either use the new operator or the malloc (memory allocate) operator: in your case malloc is the way to go. The whole explanation is quite long winded, I suggest to get a proper course about memory allocation, heap vs stack space and pointers, it’s not something that can be explained on a forum thread.

[f-peri]

ok, thanks for your reply. I will do my homework.