[hotwatermorning]

IXWebSocket unconditionally reset the caller's C++ standard to 11, including in the CLI and test directories. The original proposed boolean settings also omitted CACHE, producing list values instead of valid boolean defaults.

Use conditional defaults that respect command-line cache values and normal variables inherited through add_subdirectory. Keep C++11 as the library's default and minimum, reject C++98 explicitly, and correct the CMAKE_CXX_STANDARD_REQUIRED variable name. The CLI and tests now inherit the selected standard; the vendored test framework retains its existing C++14 minimum.

Default compile-command export before project() initializes that cache entry, while honoring explicit cache, parent-project, and environment settings. No global caller settings are forced into the cache.

Merged current master and added a configure-time regression test that embeds the library with C++17, STANDARD_REQUIRED=OFF, EXTENSIONS=ON, and compile-command export OFF, then verifies the library, CLI, and a test target retain those settings. Document the supported options.

Validation:

• Default C++11 library/CLI build: full suite 23/23 passing.
• Explicit C++17/OpenSSL build, GNU extensions ON, STANDARD_REQUIRED=OFF, compile-command export OFF: full suite 26/26 passing.
• Linux GCC C++17 unity build without TLS/zlib: full suite 23/23 passing.
• C++20 library/CLI build passes.
• C++98 configuration fails with the expected minimum-standard diagnostic.
• Compile database enabled by default; cache, parent-project, and environment OFF settings respected.
• Strict compiler warnings enabled for the C++11/C++17 builds; git diff --check passes.

[rh101]

How about this instead?

set(_IXWEBSOCKET_MIN_CXX_STD 11)
if (NOT DEFINED CMAKE_CXX_STANDARD)
    set(CMAKE_CXX_STANDARD ${_IXWEBSOCKET_MIN_CXX_STD})
endif()
if (CMAKE_CXX_STANDARD LESS ${_IXWEBSOCKET_MIN_CXX_STD})
    message(FATAL_ERROR "IXWebsocket requires c++ std >= ${_IXWEBSOCKET_MIN_CXX_STD}")
endif()

if(NOT DEFINED CMAKE_CXX_STANDARD_REQUIRED)
    set(CMAKE_CXX_STANDARD_REQUIRED ON)
endif()

if(NOT DEFINED CMAKE_CXX_EXTENSIONS)
    set(CMAKE_CXX_EXTENSIONS OFF)
endif()

[bsergean]

thanks @rh101 and @hotwatermorning ; finally merged this with a small change