Convert uint16_t array to char array - C++

Question

I'd like to convert

uint16_t status[8]; // change the values depend on the relay status: 0 or 1

to string containing a formatted representation of the eight status numbers seperated with commas e.g. status[0] = 0, status 1 = 0 ... so on, status[7] = 0 ---string--> "0, 0, 0, 0, 0, 0, 0, 0"

When I use snprintf function it returns me "1073670272" in debug mqtt in node in node-red. node-red debug message: 1073670272 value

    // ...
uint16_t status[8];
char str[80];
long lastMsg = 0;
// ...
// loop ()
void loop() {
  mb.task();
  yield();
  
  if (!client.connected()) {
    reconnect();
  }
  client.loop();

 long now = millis();
  if (now - lastMsg > 3000) {
    lastMsg = now;
  mb.readHreg(SLAVE_ID, 0x0001, status, 8, cbWrite); 
sprintf(str, "%u", status);
 client.publish("device1/relaysChannelStatus", str);
  }
}

When I print out status table before converting it with sprintf function it returns eight 0: Serial port screenshot

for (int a=0; a<8; a++)
  {
    
  Serial.print(status[a]);
  }

PubSub functions requirements:

boolean publish(const char* topic, const char* payload);
boolean publish(const char* topic, const char* payload, boolean retained);
boolean publish(const char* topic, const uint8_t * payload, unsigned int plength);
boolean publish(const char* topic, const uint8_t * payload, unsigned int plength, boolean retained);

// @Ayxan Haqverdili

void loop() {
 long now = millis();
  if (now - lastMsg > 3000) {
    lastMsg = now;
  mb.readHreg(SLAVE_ID, 0x0001, status, 8, cbWrite);   
    auto const sz = 8;
    uint16_t status[sz]; // uint16_t status[sz] = ...;
    char str[sz * 7];
    auto p = str;
    auto off = sprintf(p, "%d", status[0]);
    p+=off;
    for (int i = 1; i < sz; ++i){
      off = sprintf(p, ", %d", status[i]);
      p += off;
    }
     client.publish("device1/relaysChannelStatus", p);
  }
  }

and it returns an empty string: "" empty string debug ""

@Barmak Shemirani

  mb.readHreg(SLAVE_ID, 0x0001, status, 8, cbWrite);
   Serial.println("BEFORE sprintf:");
  for (int a=0; a<8; a++)
  {

Serial.println(status[a]);
  }

    char statusString[20];
 sprintf(statusString, "%d", status);

 Serial.println("sprintf:");
   for (int a=0; a<8; a++)
  {

Serial.println(statusString[a]);
  }
Serial.println(statusString);

Serial port: BEFORE sprintf: 0 0 0 0 0 0 0 0 sprintf: 1 0 7 3 6 7 0 2

1073670208

What's a "char table"? Do you mean a char array? What manner of conversion are you trying to achieve? It looks like maybe you want a C string containing a formatted representation of the eight status numbers, but please be specific. — John Bollinger
– John Bollinger, Commented Oct 22, 2021 at 14:07
@JohnBollinger extacly, that's what I;d like to have I'm such a rookie. ;/ — xxxbud
– xxxbud, Commented Oct 22, 2021 at 14:08
I didn't describe just one representation, but rather a whole category of them. Again, be specific. Decimal representation as opposed to hex, octal, or other? Fixed or variable width? Space delimiters or something else? If fixed width, then leading zeroes or not? Very likely some of this would be answered already if you had shown what you have already tried, and explained why it's not producing the output you require. — John Bollinger
– John Bollinger, Commented Oct 22, 2021 at 14:12

Aykhan Hagverdili · Accepted Answer · 2021-10-22 18:50:41Z

1

Here's how you do it:

#include <stdint.h>
#include <stdio.h>

int main() {
  auto const sz = 8;
  uint16_t status[sz] = { 1, 2, 3, 4, 5, 6, 7, 8 };
  
  char str[sz * 7];
  auto p = str;
  p += sprintf(p, "%d", status[0]);

  for (int i = 1; i < sz; ++i) {
    p += sprintf(p, ", %d", status[i]);
  }

  puts(str);
}

edited Oct 22, 2021 at 18:50

answered Oct 22, 2021 at 14:52

Aykhan Hagverdili

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4 Comments

xxxbud Over a year ago

Copied it to loop() and get an error: error: expected primary-expression before '...' token 357 | uint16_t status[sz] = ...;

xxxbud Over a year ago

changed to uint16_t status[sz]; and it returns empty string: ""

Aykhan Hagverdili Over a year ago

@xxxbud obviously you need to initialize the status array yourself. Mine was an example assuming you already have the array

Aykhan Hagverdili Over a year ago

@xxxbud I updated the answer to include a complete example.

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