getting error in running cmake std Tutorial step 2 example - cmake

Question

I am totally new to cmake and its syntax .But fortunately I am able to run the cmake tutorial step 1 as per the introductions mention on below links :
https://cmake.org/cmake/help/latest/guide/tutorial/index.html
But I am totally stucked at step 2 project to run using cmake.
I have created the step 2 project and understand the syntax to link the library for doing square root of a number, But I did not understand how to run this as I am getting below error :
user#server:~/TER_CMAKE/Tutorial/step2_build$ cmake ../step2
CMake Error at CMakeLists.txt:19 (add_subdirectory):
The binary directory
/home/user/TER_CMAKE/Tutorial/step2/MathFunctions
is already used to build a source directory. It cannot be used to build
source directory
/home/user/TER_CMAKE/Tutorial/step2/MathFunctions
Specify a unique binary directory name.
-- Configuring incomplete, errors occurred!
The example is available at below location for step 2 under heading Adding a Library (Step 2)..
https://moodle.rrze.uni-erlangen.de/pluginfile.php/14829/mod_resource/content/5/CMakeTutorial.pdf
My intention is to run my example this way
step2_build$ cmake ../step2
step2_build$ cmake --build .
step2_build$ ./Tutorial 121
As I am not sure that is it good to ask this way on this platform ,But as I do not have any other guidance .I am doing this by my own .
Note: I do not wants to use any tool to run my step 2 example.I wants to run everything using command prompt and cmake command only .where I can understand the cmake .
Edit:
Adding my CMakeLists.txt =
cmake_minimum_required(VERSION 3.5)
#set the project name
project(Tutorial VERSION 1.0)
#specify the c++ std
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 the version number to the source code
configure_file(TutorialConfig.h.in TutorialConfig.h)
#add the MathFunctions Library
add_subdirectory(MathFunctions)
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.cpp)
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_LIBS}
)
My Source tutorial.cpp file:
#include <iostream>
#include <cmath>
#include <cstdlib>
#include <string>
#ifdef USE_MYMATH
#include "MathFunctions.h"
#endif
#include "TutorialConfig.h"
using namespace std;
int main(int argc, char* argv[])
{
if (argc < 2) {
cout << "Usage: " << argv[0] << " number" << endl;
return 1;
}
// convert input to double
const double inputValue = atof(argv[1]);
// calculate square root
#ifdef USE_MYMATH
const double outputValue = mysqrt(inputValue);
#else
const double outputValue = sqrt(inputValue);
#endif
cout << "The square root of " << inputValue << " is " << outputValue << endl;
return 0;
}
ToturialConfig.h.in file :
#define Tutorial_VERSION_MAJOR #Tutorial_VERSION_MAJOR#
#define Tutorial_VERSION_MINOR #Tutorial_VERSION_MINOR#
#cmakedefine USE_MYMATH
EDIT:
Step2 has a folder MathFuctions,Which has Cmake file mysqrt.cpp file
/TER_CMAKE/Tutorial/step2/MathFunctions/CMakeLists.txt
add_library(MathFunctions mysqrt.cpp)
/TER_CMAKE/Tutorial/step2/MathFunctions/mysqrt.cpp
#include <iostream>
// a hack square root calculation using simple operations
double mysqrt(double x)
{
if (x <= 0) {
return 0;
}
double result = x;
// do ten iterations
for (int i = 0; i < 10; ++i) {
if (result <= 0) {
result = 0.1;
}
double delta = x - (result * result);
result = result + 0.5 * delta / result;
std::cout << "Computing sqrt of " << x << " to be " << result << std::endl;
}
return result;
}

Answer 1

In case USE_MYMATH variable is set add_subdirectory(MathFunctions) is invoked twice. You need to decide and remove one of the occurrences on lines 16 and 19 in you CMakeLists.txt.

Answer 2

Two issues I can see:
You're adding the subdirectory "MathFunctions" twice when you configure the build with -DUSE_MYMATH=ON. This is why you are getting "CMake Error at CMakeLists.txt:19 (add_subdirectory):"
To fix, remove
#add the MathFunctions Library
add_subdirectory(MathFunctions)
and rely on
if(USE_MYMATH)
add_subdirectory(MathFunctions)
list(APPEND EXTRA_LIBS MathFunctions)
list(APPEND EXTRA_INCLUDES "${PROJECT_SOURCE_DIR}/MathFunctions")
endif()
In your CMakeLists.txt file, you are doing
target_include_directories(Tutorial PUBLIC
"${PROJECT_BINARY_DIR}"
${EXTRA_LIBS}
)
Instead of
${EXTRA_LIBS}
It should be
${EXTRA_INCLUDES}

Answer 3

in Discourse Cmake Org -- help with tutorial step 2
Josef Angstenberger
jtxa said
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?
Blockquote
Marshallb's solution will solve nahesh relkar's problem
Loading Step2/CMakeLists.txt and Step3/CMakeLists.txt into vimdiff helped me to fix mine