CMake unable to determine linker language with C

Question

I m attempting to run a cmake hello world program on Windows 7 x64 with both Visual Studio 2010 and Cygwin  but can t seem to get either to work  My directory structure is as follows   HelloWorld -- CMakeLists txt -- src  -- -- CMakeLists txt -- -- main cpp -- build    I do a cd build followed by a cmake     and get an error stating that   CMake Error  CMake can not determine linker language for target helloworld CMake Error  Cannot determine link language for target  helloworld     However  if I change the extension of main cpp to main c both on my filsystem and in src CMakeLists txt everything works as expected  This is the case running from both the Visual Studio Command Prompt  Visual Studio Solution Generator  and the Cygwin Terminal  Unix Makefiles Generator    Any idea why this code wouldn t work   CMakeLists txt  PROJECT HelloWorld C  cmake minimum required VERSION 2 8     include the cmake modules directory set CMAKE MODULE PATH   HelloWorld SOURCE DIR  cmake   CMAKE MODULE PATH    add subdirectory src    src CMakeLists txt    Include the directory itself as a path to include directories set CMAKE INCLUDE CURRENT DIR ON     Create a variable called helloworld SOURCES containing all  cpp files  set HelloWorld SOURCES main cpp     Create an executable file called helloworld from sources  add executable hello   HelloWorld SOURCES      src main cpp  int main       return 0

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I managed to solve mine  by changing   add executable file1 cpp    to   add executable ProjectName file1 cpp

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Confusing as it might be  the error also happens when a cpp file included in the project does not exist   If you list your source files in CMakeLists txt and mistakenly type a file name then you get this error

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A bit unrelated answer to OP but for people like me with a somewhat similar problem    Use Case  Ubuntu  C  Clion  Auto-completion    I had the same error       CMake Error  Cannot determine link language for target  hello     set target properties hello PROPERTIES LINKER LANGUAGE C  help fixes that problem but the headers aren t included to the project and the autocompletion wont work   This is what i had  cmake minimum required VERSION 3 5   project hello   set CMAKE CXX FLAGS    CMAKE CXX FLAGS  -std c  11    set SOURCE FILES      add executable hello   SOURCE FILES    set target properties hello PROPERTIES LINKER LANGUAGE C    No errors but not what i needed  i realized including a single file as source will get me autocompletion as well as it will set the linker to C   cmake minimum required VERSION 3 5   project hello   set CMAKE CXX FLAGS    CMAKE CXX FLAGS  -std c  11    set SOURCE FILES   1 helloworld c   add executable hello   SOURCE FILES

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By default the JNI Native folder is named as jni   Renaming it to cpp fixed the issue

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Try changing  PROJECT HelloWorld C    into  PROJECT HelloWorld C CXX    or just  PROJECT HelloWorld    See  http   www cmake org cmake help v2 8 8 cmake html command project

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I also got the error you mention   CMake Error  CMake can not determine linker language for target helloworld CMake Error  Cannot determine link language for target  helloworld     In my case this was due to having C   files with the  cc extension   If CMake is unable to determine the language of the code correctly you can use the following   set target properties hello PROPERTIES LINKER LANGUAGE CXX    The accepted answer that suggests appending the language to the project   statement simply adds more strict checking for what language is used  according to the documentation   but it wasn t helpful to me      Optionally you can specify which languages your project supports    Example languages are CXX  i e  C     C  Fortran  etc  By default C   and CXX are enabled  E g  if you do not have a C   compiler  you can   disable the check for it by explicitly listing the languages you want   to support  e g  C  By using the special language  NONE  all checks   for any language can be disabled  If a variable exists called   CMAKE PROJECT  INCLUDE FILE  the file pointed to by that   variable will be included as the last step of the project command

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In my case  it was just because there were no source file in the target  All of my library was template with source code in the header  Adding an empty file cpp solved the problem

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I want to add another solution in case a library without any source files shall be build  Such libraries are also known as header only libraries  By default add library expects at least one source file added or otherwise the mentioned error occurs  Since header only libraries are quite common  cmake has the INTERFACE keyword to build such libraries  The INTERFACE keyword is used as shown below and it eliminates the need for empty source files added to the library  add library myLibrary INTERFACE  target include directories myLibrary INTERFACE  CMAKE CURRENT SOURCE DIR    The example above would build a header only library including all header files in the same directory as the CMakeLists txt  Replace  CMAKE CURRENT SOURCE DIR  with a path in case your header files are in a different directory than the CMakeLists txt file  Have a look at this blog post or the cmake documentation for further info regarding header only libraries and cmake

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In my case  implementing a member function of a class in a header file cause this error  Separating interface  in x h file  and implementation  in x cpp file  solves the problem

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I also faced a similar error while compiling my C-based code  I fixed the issue by correcting the source file path in my cmake file   Please check the source file path of each source file mentioned in your cmake file  This might help you too

[c++] CMake unable to determine linker language with C++

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