ESP-IDF Project Structure Issue: 'Undefined Reference to Function' Error

Question

I've started a project based on the ESP-IDF example 'blink' and am trying to reorganize it into a more structured format. My goal is to have a project structure like this:

BLINK/
├── components/
│   ├── arduino/
│   ├── lib1/
│   │   ├── include/
│   │   │   └── foo.h
│   │   ├── src/
│   │   │   └── foo.c
│   │   └── CMakeLists.txt
│   └── ...
├── main/
│   └── main.c
├── CMakeLists.txt
├── sdkconfig
└── README.md

I modified main.c in the main folder as follows:

#include <stdio.h>
#include "sdkconfig.h"
#include "../components/lib1/include/foo.h"

void app_main() {
    printfoo(); 
    while (1) {      
    }
}

Here are the contents of the files in my lib1 component:

• foo.h:

  #include <stdio.h>
  void printfoo();
  

• foo.c:

  #include "foo.h"
  
  void printfoo() {
      printf("Hello from Foo\r\n");
  }
  

• CMakeLists.txt in BLINK/components/lib1/:

  set(COMPONENT_SRCS "foo.c")
  set(COMPONENT_ADD_INCLUDEDIRS "." "include")
  register_component()
  

When I compile the project, I get the following error:

main.c:6: undefined reference to `printfoo'

I know that this error output means that linker couldn't find definition of the function printfoo which located in foo.c

Any suggestions on what might be causing this error and how to resolve it?

update: I am using ESP-IDF version v3.3.6.

I have followed the ESP32 guide on Component CMakeLists Files but am still encountering this issue.

Answer 1

General
I think the problem is that you set you're source to foo.c, but the that file is at src/foo.c. Thus, the source file isn't added and as a consequence, the function isn't implemented.

ESP-IDF v3.3.6
In ESP-IDF v3.3.6, the following CMakeLists.txt should work:

set(COMPONENT_SRCS "src/foo.c")
set(COMPONENT_ADD_INCLUDEDIRS "include")
register_component()

More information/documentatio v3.3.6

ESP-IDF v5.x
In version v5.x, SRCS and INCLUDE_DIRS are commonly used instead of COMPONENT_SRCS and COMPONENT_ADD_INCLUDEDIRS respectively. In ESP-IDF v5.x, the following CMakeLists.txt should work:

idf_component_register(SRCS "src/foo.c"
                       INCLUDE_DIRS "include")

More information/documentatio v5.x

General
Then, in main, you should be able to include foo.h in the following way:

#include "foo.h"

Answer 2

ESP-IDF v3.3.6

I solved this issue, by add a file named component.mk to the project with the following content:

COMPONENT_ADD_INCLUDEDIRS := .

Beside this addition, i modifed the project structure as shown below:

BLINK/
├── components/
│   ├── arduino/
│   ├── lib1/
│   │   ├── foo.h
│   │   ├── foo.c
│   │   ├── CMakeLists.txt
│   │   └── component.mk
│   └── ...
├── main/
│   └── main.c
├── CMakeLists.txt
├── sdkconfig
└── README.md

In the lib1 component of the project, the final contents of the files should be as follows:

• foo.h:

  #include <stdio.h>
  void printfoo();
  

• foo.c:

  #include "foo.h"
  
  void printfoo() {
      printf("Hello from Foo\r\n");
  }
  

• CMakeLists.txt in BLINK/components/lib1/:

    set(COMPONENT_SRCS "foo.c")
    set(COMPONENT_ADD_INCLUDEDIRS "." )
    register_component()
  
  

• component.mk in BLINK/components/lib1/:

  COMPONENT_ADD_INCLUDEDIRS := .
  

Finally, main application code (app_main) in BLINK/main/main.c should include the necessary headers and invoke printfoo() as follows:

#include <stdio.h>
#include "sdkconfig.h"
#include "foo.h"

void app_main() {
    printfoo(); 
    while (1) {      
    }
}