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I am using Arduino. I would like to append a String object to an array of characters.

String msg = "ddeeff"

char charArr[1600];

//assume charArr already contains some string
//How can I do something like this to append String to charArray?
charArr = charArr + msg;
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2 Answers 2

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This will work for Arduino String object. 

strcat( charArr, msg.c_str() );

String object msg gets converted into an array of characters with the String method c_str(). Then, you can use strcat() to append the 2 arrays of characters.

As mentioned by Rakete1111, it is undefined behavior if charArr is not big enough

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2 Comments

Be careful though, it is undefined behavior if charArr is not big enough.
char charArr[1600]; might rather be too big for a "standard" Arduino UNO, depending on other local variable requirements etc. Be careful in that direction, too. Behavior is undefined as well. ;)
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String has a operator+ which takes a const char*, and it also has a c_str() function, which converts it to a const char*.

You can combine them to get the desired result:

String temp = charrArr + msg; //Store result in a String

//Copy every character
std::strncpy(charArr, temp.c_str(), sizeof(charrArr));
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1 Comment

Now charArr may not contain the terminating '\0'.

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