Create library in Arduino IDE

Projects Programming
1

I'm trying to create library this is my code
Why I get on :
undefined reference to addTwoInts(signed char, int)'`

Test.h file

#include "stdint.h"

#ifndef TEST_H
#define TEST_H
void addTwoInts(int8_t a, int b);
#endif

Test.c file

#include "Test.h"
#include "stdint.h"
void addTwoInts(int8_t a, int b)
{
  printf("The result is =%d", a + b);
}

main arduino

#include "Test.h"
void setup() 
{
  Serial.begin(9600);
  addTwoInts(4,3);
}
void loop() {}
2

Where did you put Test.h and Test.c?

3

In the same folder.

4

Hi @alex_al. The reason for the error is that, after some minor preprocessing, the .ino files of the sketch are compiled as C++, but Test.c is compiled as C because you used the .c file extension.

The easiest fix is to simply change the file name to Test.cpp. That will cause it to be compiled as C++. You will find that convenient because most of the Arduino core API and libraries are also C++, so writing your code in C++ will allow you to use them.

If you really do want to use C, you can wrap the declarations in extern "C" {}:

extern "C" {
#include "Test.h"
}
5

Hi @in0 , use this

"C" {}

in Test.c ? because I get on expected identifier or '(' before string constant

6

No. Replace this line in your .ino file:

#include "Test.h"

with this:

extern "C" {
#include "Test.h"
}

You could also wrap the declarations in the header file instead, using this common construct:

#ifdef __cplusplus
extern "C" {
#endif

// all of your legacy C code here

#ifdef __cplusplus
}
#endif
7

The header file be like this ?

#ifdef __cplusplus
extern "C" {
#endif

#include "stdint.h"

#ifndef TEST_H
#define TEST_H
void addTwoInts(int8_t a, int b);
#endif

#ifdef __cplusplus
}
#endif
8

Better like this:

#ifndef TEST_H
#define TEST_H

#include "stdint.h"

#ifdef __cplusplus
extern "C" {
#endif

void addTwoInts(int8_t a, int b);

#ifdef __cplusplus
}
#endif

#endif
9

Thank you so much !

10

You are welcome. Best wishes for success with your library!

13

Hello, other relevant question. I have lib contains on many functions look like this
mainlib.h // in side this file mainlib.h I have

lib1.h
bib2.h
lib3.h
// functions

every think work well but When import this mainlib.h inside
the sketch I get on all this headers

#include <mainlib.h>  
#include <lib1.h>
#include <bib2.h>
#include <lib3.h>

I need to import and show just the main library "mainlib.h "

14

Topics merged

15

OK thanks :slight_smile:

16

Why did you create a new topic, particularly when you originally added your new question here only to delete it ?

17

Because I got the answer to my previous question so I wanted to add this question as a new topic.

18

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