C++ (GCC / Clang): Warn on unused function result/return for safety

warn_unused_result.cpp

// https://gcc.gnu.org/onlinedocs/gcc-4.7.2/gcc/Function-Attributes.html
// https://infektor.net/posts/2017-01-19-using-cpp17-attributes-today.html
// Compiler flags: -Wall -Werror -Wextra -pedantic -Wunused-result -std=c++11
// Suggested macro names: HANDLE_OUTPUT / NODISCARD / MUST_HANDLE

#define HANDLE_OUTPUT __attribute__((warn_unused_result))

HANDLE_OUTPUT int critical_func()
{
    return 1234;
}

template<typename ... Args>
void ignore(Args && ...)
{
}

int use_critical_func()
{
    // This will cause the warning: [x86-64 gcc 7.2 #1] error: ignoring return value of 'int critical_func()',
    // declared with attribute warn_unused_result [-Werror=unused-result]
    //critical_func();

    // This will pass
    ignore(critical_func());

    return 0;
}