Problem using strcat function.

Using Arduino Programming Questions
1

I also have a weird problem related to strcat. I have two global char array for example char str1[12] and char str2[10], now in my code some data are given from user and should be stored into these arrays. This is the process:

  • get data1 and data2

in the code:

strcat(str1, "HB");
strcat(str1, data1);
Serial.println(str1); //HB1234556

strcat(str2,"UR");
strcat(str2, data2);
Serial.println(str2); //UR10302493
Serial.println(str1); //HB1234556UR10302493

But the problem is that when I put data1 into str1 and I print it, its value is correct, and also value of str2 is OK, but when I print value of str1 after str2 value is set, I see that str2 is concatenated at the end of str1!! What can be the problem??

2

You're probably running off the end of one array.
If you posted your code, we could tell for sure.

3

TheMemberFormerlyKnownAsAWOL:
You're probably running off the end of one array.
If you posted your code, we could tell for sure.

this is part of my code:

char deviceid[14];
char mobile_id[13];

setup
{
....
}

loop
{
if ( command_type == 10)
{

WifiSettings = 1;
const char *router_ssid = root["data_val1"]; //from parsing json data
const char *router_pass = root["data_val2"];
const char *user_id = root["user_id"];

if (user_id != NULL)
{
strcpy(mobile_id, "UR");
strcat(mobile_id, user_id);
}

Serial.print("userid: ");
Serial.println(mobile_id); //here mobileid is OK

char MACAddr[17];
strcpy(MACAddr, WiFi.macAddress().c_str());

String device_id = "HB";

int k = 2;
for (int i = 0; i < 17; i++)
{
if (i != k)
{
device_id += MACAddr*;*

  • }*
  • else*
  • k += 3;*
  • }*
  • if (device_id.length() > 1 && device_id.length() <= 26)*
  • strcpy(deviceid, device_id.c_str());*
  • Serial.println(deviceid); //deviceid is OK*
  • Serial.println(mobile_id); //but here mobileid is concatenated with deviceid!!*
  • // JSON response*
  • String s = "HTTP/1.1 200 OK\r\n";*
  • s += "Content-Type: application/json\r\n\r\n";*
  • s += "{"c_type":";*
  • s += String(command_type);*
  • s += ","Status":"";*
  • s += String(Status);*
  • s += "","hub_id":"";*
  • s += device_id;*
  • s += ""}\r\n";*
  • s += "\n";*
  • WaitResponse = 1;*
  • client.print(s);*
  • delay(1);*
  • client.stop();*
    }
    }
4

...and that's why we ask you to use code tags when posting code.

5