Build a boost project using cmake in msvc - c++

Question

I have written a code to read a compressed file directly. I have to build it using Cmake. This is my only source file, uncompress.cpp
#include <iostream>
#include <vector>
#include <boost/iostreams/filtering_stream.hpp>
#include <boost/iostreams/filter/bzip2.hpp>
// cl /EHsc uncompress.cpp
std::vector<char> & readline(std::istream & stream, std::vector<char> & container) {
char c;
container.clear();
while (stream && stream.get(c)) {
container.push_back(c);
if (c == '\n') break;
}
return container;
}
int main () {
boost::iostreams::filtering_istream in;
boost::iostreams::filtering_istream cinn(std::cin);
in.push(boost::iostreams::bzip2_decompressor());
in.push(cinn);
std::vector<char> line;
while (readline(in, line).size() != 0) {
std::string str(line.begin(), line.end());
std::cout << "--" << str ;
}
}
My CMakeLists.txt includes
cmake_minimum_required (VERSION 2.8.9)
project (reader-demo CXX C)
find_package (Boost COMPONENTS iostreams zlib REQUIRED)
include_directories (${Boost_INCLUDE_DIR} )
add_executable(reader uncompress.cpp)
target_link_libraries(reader ${Boost_LIBRARIES})
my cmake command is:
cmake -G "NMake Makefiles" .
This throws the error boost_zlib not found during cmake
Could not find the following Boost libraries:
boost_zlib
I have the following zlib library built into all paths are set properly:
NOTE if I change the CMakeLists.txt to this. it works fine. But I can't understand how :/
cmake_minimum_required (VERSION 2.8.9)
project (reader-demo CXX C)
add_executable(reader uncompress.cpp)
it works fine as expected. reader.exe is make and that works fine.
My question is: why is it not able to find boost_zlib the time I mention it in cmake and why is it working fine when I remove the target_link_libraries().

Answer 1

Expanding my comments to an answer:
zlib is not a registered Boost component although the Boost build process for boost_iostreams lib generates a boost_zlib and boost_bzip2 library. Both are internally generated and linked to. The CMake module FindBoost.cmake that is called when you add find_package(Boost COMPONENTS iostreams zlib REQUIRED) to your CMakeLists.txt file does not know about these libraries.
To answer the first part of the question:
remove zlib from your find_package call.
After doing so delete the CMakeCache.txt file because the values of a Boost search are cached in CMake.
To answer the second part of the question:
You removed the Boost stuff from the CMakeLists.txt but presumably did not delete the CMakeCache.txt. It might still contain the necessary Boost entries for the compiler/linker and that may be the reason why it works in the second call.
The libraries you showed in the image are the (multithreaded) static libraries and the import libraries for the DLLs.
To use the static libraries
you need to add set(Boost_USE_STATIC_LIBS ON) to your CMakeLists.txt file before calling find_package(Boost ...).
To use the Shared Objects (SO)/Dynamic Link Libraries (DLL)
you don't need to add anything to your CMakeLists.txt file before calling find_package(Boost ...), as dynamic link libraries are chosen by default. But to run the executable the directory that contains the DLLs must be added to the PATH environment variable.
NB:
Please remove the call to include_directories(${Boost_INCLUDE_DIR}) and add after the definition of your target
add_executable(reader uncompress)
target_include_directories(reader PRIVATE ${Boost_INCLUDE_DIRS})
Note the trailing S in the variable name. This variable is assigned a value in the find_package(Boost ..) call, the other variable is used to look up the include directory of Boost and is an input to the FindBoost module. Doing so you add the include directories to the target only but not to the global environment.
Finally you should add -DBOOST_ROOT=<path_to_your_Boost_installation> to your CMake command line call to make sure Boost is found regardless of a non standard installation directory.
For extended information about find_package(Boost ...) please see the documentation