Using CMake to find symbols in libraries - linux

Question

I am trying to use CMake to find if an external library depends on another library.
Example: the HDF5 library can be optionally linked with zlib
In Linux, this can be found with
readelf -Ws /usr/local/lib/libhdf5.so | grep inflateEnd
54: 0000000000000000 0 FUNC GLOBAL DEFAULT UND inflateEnd
With CMake it seems this can be found with CheckLibraryExists
https://cmake.org/cmake/help/v3.0/module/CheckLibraryExists.html
In Cmake script
set(CMAKE_REQUIRED_LIBRARIES ${HDF5_LIBRARY})
check_library_exists(${HDF5_LIBRARY} inflateEnd "" NEED_ZLIB)
message(${NEED_ZLIB})
if (NEED_ZLIB)
message("-- ZLIB library is needed...")
else()
message("-- ZLIB library is not needed...")
endif()
output is not found
-- Looking for inflateEnd in /usr/local/lib/libhdf5.so - not found
-- ZLIB library is not needed...
because of this I did the Cmake version of using readelf, that finds the symbol
but, still would like to know why the above Cmake script fails :-)
the working version is
set(have_read_symbols "no")
find_program(read_symbols_prg readelf)
if (${read_symbols_prg} MATCHES "readelf")
set(have_read_symbols "yes")
message("-- Readelf program found: " ${read_symbols_prg})
execute_process(COMMAND ${read_symbols_prg} -Ws ${HDF5_LIBRARY} OUTPUT_FILE ${CMAKE_CURRENT_BINARY_DIR}/symbols.txt)
endif()
if (${have_read_symbols} MATCHES "yes")
message("-- Detecting if HDF5 library ${HDF5_LIBRARY} needs the ZLIB library...")
file(STRINGS ${CMAKE_CURRENT_BINARY_DIR}/symbols.txt NEED_ZLIB REGEX "inflateEnd")
if (NEED_ZLIB)
message("${color_blue}-- ZLIB library is needed...${color_reset}")
else()
message("-- ZLIB library is not needed...")
endif(NEED_ZLIB)
endif()
that finds the symbol
-- Detecting if HDF5 library /usr/local/lib/libhdf5.so needs the ZLIB library...
-- ZLIB library is needed...

Answer 1

Ok, The Cmake documentation for checkLibraryExists() is short on details on how this is accomplished, they just say "Check if the function exists".
checkLibraryExists() tries to link a test program, and depending on success or not, the output variable parameter is set to value 1 or empty.
In this case, the symbol to look must be one that is defined in libhdf5.so only with using the zlib library. There is one and only one symbol for this case, a structure named "H5Z_DEFLATE" that is added to the library depending on a #ifdef for the zlib case.
So, this does the trick
check_library_exists(${HDF5_LIBRARY} H5Z_DEFLATE "" NEED_ZLIB)
However for the Windows case using Visual Studio this is error prone, because for check_library_exists() to detect it, Visual Studio must set an option as additional dependencies the zlib library, and this is not a requirement for the library to build successfully. So, if this option is set, check_library_exists detects the dependency, if not set, it does not.