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 eg 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

Answer 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);
}