Try this
void setup()
{
Serial.begin(115200);
char Buff1[30] = "abcdefghijklmnopqrst";
char Buff2[30] = "123456abcdefghijklmnopqrst";
if (strcmp(Buff1, Buff2 + 6) == 0)
{
Serial.println("COMPARE TRUE");
}
else
{
Serial.println("COMPARE FALSE");
}
}
void loop()
{
}