Concatenating strings together in Arduino

Question

I want to do something similar to this:

char* a = (char*)msg[0];
char* b = (char*)msg[1];
char* c = a + "," + b;

Where msg is an array of int.

N.B.: This is Arduino C++, not regular C++.

I can't use it in arduino.. I don't know why compiler doesn't know it — Jongz Puangput, Jul 29 '14 at 09:51
@JongzPuangput are you sure your compiler understands C++, not C? — bereal, Jul 29 '14 at 09:53
Please add the definition of `msg` in your code. Is it an array of strings? — barak manos, Jul 29 '14 at 09:53
@JongzPuangput: Then you're not using C++ but C, which is a completely different language. — datenwolf, Jul 29 '14 at 09:53
@JongzPuangput and don't you think you should have mentioned that you are using a freestanding (in contrast with a hosted) implementation of C++? Have you tried researching at all? The almost-equivalent [`String` class](http://arduino.cc/en/Reference/string) is ***trivial*** to find in the documentation. — The Paramagnetic Croissant, Jul 29 '14 at 09:53
@bereal, Arduino's C++ installation is not a hosted environment, it lacks quite a bit of the standard library. — The Paramagnetic Croissant, Jul 29 '14 at 09:54
@datenwolf no, probably not. Arduino's C++ setup does not have `std::string`. — The Paramagnetic Croissant, Jul 29 '14 at 09:54
Possible duplicate of [C++ string and Arduino String. How to combine them?](http://stackoverflow.com/questions/9839990/c-string-and-arduino-string-how-to-combine-them) — The Paramagnetic Croissant, Jul 29 '14 at 09:56
Why are you trying to convert two `int`s to two `char*`s and then add them together. Something is suspiciously wrong here. Perhaps you should add all the relevant information and tell us what it is exactly that you're trying to do... — barak manos, Jul 29 '14 at 09:56
I want to add comma in between and set in the function that require char* — Jongz Puangput, Jul 29 '14 at 09:58
Not good enough. Are you trying to take two `int` values and put them inside a string, where they are separated by a comma? — barak manos, Jul 29 '14 at 10:01
You shouldn't edit the body of the question with the answer. Instead, either make a new answer and accept it or accept the answer that helped you. — Rapptz, Jul 29 '14 at 10:14

score 2 · Accepted Answer · answered Jul 29 '14 at 10:00

Arduino doesn't use std::string, instead it uses String (note the capital S and dropped std::). They're used the same way as std::string for the most part. So basically you should just be able to do this:

String a("hello");
String b(" world");
c = a + b;

If you want to convert an integer to a String, it has a constructor to do just that, e.g.:

String a = String(msg[0]);
String b = String(msg[1]);

You can find more examples here and here.

score 1 · Answer 2 · answered Jul 29 '14 at 09:51

1

See strcat. You seem to be programming C, not C++. This should be covered in the most basic tutorials.

answered Jul 29 '14 at 09:51

Daniel Albuschat

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am I misunderstand?? don't arduino is develop in c++?? – Jongz Puangput Jul 29 '14 at 09:52
@JongzPuangput Usually, when you write code that looks like C, people say "this is not C++". But technically, a lot of C code is also valid C++. Not sure yours is, because I don't know what `msg` is, but the cast to `char*` is likely to be wrong. – juanchopanza Jul 29 '14 at 09:55
1

@JongzPuangput That doesn't mean it is not wrong to cast. But there is not enough information to know for sure. – juanchopanza Jul 29 '14 at 09:58

score 1 · Answer 3 · answered Jul 29 '14 at 10:21

1

SOLUTION

so here is my solution thank everyone.

  String a = String(msg[0]);
  String b = String(msg[1]);
  String c = a + "," + b;
  char* d;
  c.toCharArray(d,c.length());

  mclient.publish("topic1/sensorAck",d);

answered Jul 29 '14 at 10:21

Jongz Puangput

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Concatenating strings together in Arduino

3 Answers3