How can I concatenate these two values as a string?

Question

I've tried all the supposed solutions for the exact error, pasted into google, that I could find on every forum including this one and no matter the alleged solution I will either get the error about unsigned int to char*, the error below, or invalid pointers.

Why is this platform so completely unfriendly in data type conversion? It's almost as if the creator/s never wanted any data types to be able convert.

Here's my code that is apparently useless:

 char* DeviceName = "Device-" + ESP.getChipId();
 wifiManager.autoConnect(DeviceName);

Error: invalid conversion from 'const char*' to 'char*' [-fpermissive] char* DeviceName = "Device-" + ESP.getChipId();

Then I tried to use the pointers, but I have no idea what I'm doing and I keep getting invalid pointer errors, and/or invalid conversion errors.

• Mikael Patel: Hint: Try using sprintf(). cplusplus.com/reference/cstdio/sprintf
• Ethan Aaron Vandal: char buffer [50]; char DeviceName = sprintf(buffer, "Device-%d", ESP.getChipId()); wifiManager.autoConnect(DeviceName)
• Ethan Aaron Vandal: error: invalid conversion from 'char' to 'const char*' [-fpermissive] wifiManager.autoConnect(DeviceName)

Answer 1

You can use the c function sprintf(, , ...) The char array has to be big enough to hold your text plus a null to terminate the string.

#include <Arduino.h>
void setup() {
 Serial.begin(115200);
 delay(1000);
 char out[20];
 sprintf(out, "Device-%08X",ESP.getChipId()); // %08X\n formats the hex and pads with 0s.
 Serial.println(out);
}
void loop() {}

Output:

Device-005D4D9D

• Ethan Aaron Vandal: Thank you! I tried this and it does output a numeric ID, but I wanted the string ID. ESP8266 Chip ID = 005D4D9D <- this should be the ID... Device-6114717 <- not the numeric conversion here
• SEngstrom: you are welcome - helpful user changed the format string to output 8 hex digits instead since that is what you seem to be looking for.
• Ethan Aaron Vandal: Learning is good. To eliminate extra characters you can also use sprintf(out, "Device-%X",ESP.getChipId())