Include Files in Segger Embedded Studio - c

Question

I am just starting out with Segger Embedded Studio. Right now trying to call a function of a included header file. The file seems to be included since it shows up in the dependencies. For now I simply included the header and C-File in the project directory.
The included Header- and C-Files are simply:
//##### Header-File ######
#ifndef TEST_H_
#define TEST_H_
void printText(void);
#endif //TEST_H_
and:
//###### C-File #########
#include <test.h>
#include <stdio.h>
#include <stdlib.h>
void printText(void)
{
printf("Hello");
}
But when I try to call the printText Function in my main I get the error:
"Undefined Symbol: printText".
Why is the function not recognized?

Answer 1

"Undefined symbol" is a linker error. You are not linking the object code containing the definition of printText().
It is not an issue with the header file; including a header file does not cause the associated code to be linked - that is just the declaration so the compiler knows what the interface looks like. It is the linker than combines the separately compiled object code to form a program. You have not told the linker to use the object code containing printText(), and you have not told your IDE project to compile it to generate that object code.
The project tree clearly shows that only main.c is included in your project; you need to add the C file containing printText() too.
The concept of separate compilation and linking is what you need to grasp here.

Answer 2

Thank you Clifford for your answer. You are right I had some miss-conceptions about which files will be linked while building the project. In the special case of segger embedded studio there are, as I know by now, two ways to reference extern files.
Adding the files to the sources files folder is straight forward, but must be done separately for each project you want to use the respective files.
For frequently used files it is beneficial to create a dedicated library solution. Such a library can then be imported to any solution by choosing "add existing project". This will add all files of the library to your current solution (and show them in the project-tree). Now click the tab project -> dependencies. Your library should show up here. By acitivating the check box the linker will compile the referenced project upon builing your solution, allowing for the usage of your library functions.
Adding and linking library-project to a current solution