# Help with tutorial step 2
**URL:** https://discourse.cmake.org/t/help-with-tutorial-step-2/4403
**Category:** Code
**Created:** [November 2, 2021, 3:52pm UTC](https://discourse.cmake.org/t/help-with-tutorial-step-2/4403 "2021-11-02T15:52:40Z")
**Posts on this page:** 13
**Page:** 1
### Author:  [@jamadagni](https://discourse.cmake.org/u/jamadagni)
#### Post date: [November 2, 2021, 3:52pm UTC](https://discourse.cmake.org/t/help-with-tutorial-step-2/4403/1 "2021-11-02T15:52:40Z")
Hello. I am trying to learn CMake using the Tutorial. I am at Step 2.
The contents of my main CMakeLists.txt:
```auto
cmake_minimum_required(VERSION 3.10)
# set the project name and version
project(Tutorial VERSION 1.0)
# specify the C++ standard
set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED True)
option(USE_MYMATH "Use tutorial provided math implementation" ON)
# configure a header file to pass some of the CMake settings
# to the source code
configure_file(TutorialConfig.h.in TutorialConfig.h)
if(USE_MYMATH)
add_subdirectory(MathFunctions)
list(APPEND EXTRA_LIBS MathFunctions)
list(APPEND EXTRA_INCLUDES "${PROJECT_SOURCE_DIR}/MathFunctions")
endif()
# add the executable
add_executable(Tutorial tutorial.cxx)
target_link_libraries(Tutorial PUBLIC ${EXTRA_LIBS})
# add the binary tree to the search path for include files
# so that we will find TutorialConfig.h
target_include_directories(Tutorial PUBLIC
"${PROJECT_BINARY_DIR}"
${EXTRA_INCLUDES}
)
```
Upon building I am getting the error:
```auto
Scanning dependencies of target MathFunctions
[25%] Building CXX object MathFunctions/CMakeFiles/MathFunctions.dir/mysqrt.cxx.o
[50%] Linking CXX static library libMathFunctions.a
[50%] Built target MathFunctions
Scanning dependencies of target Tutorial
[75%] Building CXX object CMakeFiles/Tutorial.dir/tutorial.cxx.o
/home/samjnaa/sr/_repos/git/cmake/Help/guide/tutorial/Step2copy/tutorial.cxx:26:30: error: use of undeclared identifier 'mysqrt'
const double outputValue = mysqrt(inputValue);
^
1 error generated.
make[2]: *** [CMakeFiles/Tutorial.dir/build.make:63: CMakeFiles/Tutorial.dir/tutorial.cxx.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:96: CMakeFiles/Tutorial.dir/all] Error 2
make: *** [Makefile:84: all] Error 2
```
Please advise as to what I’m doing wrong. Please ask if I need to post the contents of any other file as well. Thanks!
---
### Author:  [@jtxa](https://discourse.cmake.org/u/jtxa)
#### Post date: [November 2, 2021, 4:44pm UTC](https://discourse.cmake.org/t/help-with-tutorial-step-2/4403/2 "2021-11-02T16:44:02Z")
The CMake file looks perfect. Have you forgotten to add the new include to `tutorial.cxx`?
```auto
#ifdef USE_MYMATH
# include "MathFunctions.h"
#endif
```
---
### Author:  [@jamadagni](https://discourse.cmake.org/u/jamadagni)
#### Post date: [November 4, 2021, 10:55am UTC](https://discourse.cmake.org/t/help-with-tutorial-step-2/4403/3 "2021-11-04T10:55:31Z")
I have included it, nothing missing.
---
### Author:  [@jtxa](https://discourse.cmake.org/u/jtxa)
#### Post date: [November 4, 2021, 9:25pm UTC](https://discourse.cmake.org/t/help-with-tutorial-step-2/4403/4 "2021-11-04T21:25:04Z")
The files in Step3 are the expected result if you do everything from Step2.
Can you please compare your files against the ones from Step3 to see if there are any relevant differences?
---
### Author:  [@erlendaasland](https://discourse.cmake.org/u/erlendaasland)
#### Post date: [November 5, 2021, 8:44am UTC](https://discourse.cmake.org/t/help-with-tutorial-step-2/4403/5 "2021-11-05T08:44:15Z")
Can you post the contents of the `CMakeLists.txt` in the `MathFunctions` subdirectory?
---
### Author:  [@jamadagni](https://discourse.cmake.org/u/jamadagni)
#### Post date: [November 7, 2021, 10:51am UTC](https://discourse.cmake.org/t/help-with-tutorial-step-2/4403/6 "2021-11-07T10:51:46Z")
It’s just
```auto
add_library(MathFunctions mysqrt.cxx)
```
---
### Author:  [@jamadagni](https://discourse.cmake.org/u/jamadagni)
#### Post date: [November 7, 2021, 10:53am UTC](https://discourse.cmake.org/t/help-with-tutorial-step-2/4403/7 "2021-11-07T10:53:19Z")
No, there are only a couple of comment lines extra.
---
### Author:  [@jtxa](https://discourse.cmake.org/u/jtxa)
#### Post date: [November 7, 2021, 2:32pm UTC](https://discourse.cmake.org/t/help-with-tutorial-step-2/4403/8 "2021-11-07T14:32:07Z")
Based on the compiler error message, the function prototype of `mysqrt` is missing.
This can be caused by not including the header with the Prototype, including another header file with the same name but without prototype or by a misspelled function name.
Can you please add a warning into the `MathFunctions.h` to check if it really was included:
```auto
#warning Header included
```
The output of you make should look like this:
```auto
Scanning dependencies of target MathFunctions
[25%] Building CXX object MathFunctions/CMakeFiles/MathFunctions.dir/mysqrt.cxx.o
In file included from /home/u/cmake/Help/guide/tutorial/Step3/MathFunctions/mysqrt.cxx:3:
/home/u/cmake/Help/guide/tutorial/Step3/MathFunctions/MathFunctions.h:1:2: warning: #warning Header included [-Wcpp]
#warning Header included
^ ~~~~~~
[50%] Linking CXX static library libMathFunctions.a
[50%] Built target MathFunctions
Scanning dependencies of target Tutorial
[75%] Building CXX object CMakeFiles/Tutorial.dir/tutorial.cxx.o
In file included from /home/u/cmake/Help/guide/tutorial/Step3/tutorial.cxx:10:
/home/u/cmake/Help/guide/tutorial/Step3/MathFunctions/MathFunctions.h:1:2: warning: #warning Header included [-Wcpp]
#warning Header included
^ ~~~~~~
[100%] Linking CXX executable Tutorial
[100%] Built target Tutorial
```
So you can see, that the header was really included by both `.cxx` files.
---
### Author:  [@ClausKlein](https://discourse.cmake.org/u/ClausKlein)
#### Post date: [November 7, 2021, 4:14pm UTC](https://discourse.cmake.org/t/help-with-tutorial-step-2/4403/9 "2021-11-07T16:14:47Z")
Perhaps it may help if you clone the `CMake` repo and work direct with the **tutorial** :
```bash
bash-3.2$ git status .
Auf Branch develop
nichts zu committen, Arbeitsverzeichnis unverändert
bash-3.2$ git remote -v
origin https://gitlab.kitware.com/cmake/cmake.git (fetch)
origin https://gitlab.kitware.com/cmake/cmake.git (push)
bash-3.2$ pwd
/Users/clausklein/Downloads/cmake/Help/guide/tutorial
bash-3.2$ ll Step2
total 24
-rw-r--r-- 1 clausklein staff 615B 5 Jul 2020 CMakeLists.txt
drwxr-xr-x 4 clausklein staff 128B 5 Jul 2020 MathFunctions/
-rw-r--r-- 1 clausklein staff 164B 5 Jul 2020 TutorialConfig.h.in
drwxr-xr-x 6 clausklein staff 192B 5 Jul 2020 ./
-rw-r--r-- 1 clausklein staff 701B 5 Jul 2020 tutorial.cxx
drwxr-xr-x 16 clausklein staff 512B 26 Feb 2021 ../
bash-3.2$
```
---
### Author:  [@jamadagni](https://discourse.cmake.org/u/jamadagni)
#### Post date: [November 8, 2021, 11:06am UTC](https://discourse.cmake.org/t/help-with-tutorial-step-2/4403/10 "2021-11-08T11:06:01Z")
Sorry in my earlier reply I had compared only the CMakeLists.txt. Now I compared the whole directories and found my mistake:
```auto
#include "TutorialConfig.h"
#ifdef USE_MYMATH
# include "MathFunctions.h"
#endif
```
In my files I had included the `#ifdef USE_MYMATH` etc at the top of the file and hence it couldn’t read the `USE_MYMATH` from the TutorialConfig.h file…
The relevant part of the tutorial:
> in `tutorial.cxx`, include the `MathFunctions.h` header if we need it:
>
> ```auto
> #ifdef USE_MYMATH
> # include "MathFunctions.h"
> #endif
>
> ```
It would be good to have an admonishment to include this _after_ the `#include "TutorialConfig.h"` line.
Is this part from the tutorial related to the above?:
> **Exercise** : Why is it important that we configure `TutorialConfig.h.in` after the option for `USE_MYMATH`? What would happen if we inverted the two?
---
### Author:  [@jtxa](https://discourse.cmake.org/u/jtxa)
#### Post date: [November 9, 2021, 12:28am UTC](https://discourse.cmake.org/t/help-with-tutorial-step-2/4403/11 "2021-11-09T00:28:06Z")
Good to hear that the problem is identified.
The exercise refers to this CMake code:
```auto
option(USE_MYMATH "Use tutorial provided math implementation" ON)
# configure a header file to pass some of the CMake settings
# to the source code
configure_file(TutorialConfig.h.in TutorialConfig.h)
```
Which is about the same problem, but for CMake not C: Do not use a symbol before its definition.
So probably there should be added a hint or the complete code of the inclusion to the tutorial.
---
### Author:  [@jamadagni](https://discourse.cmake.org/u/jamadagni)
#### Post date: [November 9, 2021, 3:58am UTC](https://discourse.cmake.org/t/help-with-tutorial-step-2/4403/12 "2021-11-09T03:58:22Z")
Yes now I can see that and have tested it. Thanks.
---
### Author:  [@erlendaasland](https://discourse.cmake.org/u/erlendaasland)
#### Post date: [November 9, 2021, 8:39am UTC](https://discourse.cmake.org/t/help-with-tutorial-step-2/4403/13 "2021-11-09T08:39:50Z")
But this is a _CMake tutorial_, not a C tutorial. The complete code is already available, quoting from the webpage:
```
The tutorial documentation and source code for examples
can be found in the Help/guide/tutorial directory of the
CMake source code tree.
```
If a hint should be added, I would suggest adding it in the form of an exercise at the bottom of the page.