The only Boost libraries that must be built separately are:

• Boost.Filesystem
• Boost.IOStreams
• Boost.ProgramOptions
• Boost.Python (see the Boost.Python build documentation before building and installing it)
• Boost.Regex
• Boost.Serialization
• Boost.Signals
• Boost.Thread
• Boost.Wave

还有几个是可选编译的
A few libraries have optional separately-compiled binaries:

• Boost.DateTime has a binary component that is only needed if you're using its to_string/from_string or serialization features, or if you're targeting Visual C++ 6.x or Borland.
• Boost.Graph also has a binary component that is only needed if you intend to parse GraphViz files.
• Boost.Test can be used in “header-only” or “separately compiled” mode, although separate compilation is recommended for serious use.

Declaring a member function with the const keyword specifies that the function is a "read-only" function that does not modify the object for which it is called.

To declare a constant member function, place the const keyword after the closing parenthesis of the argument list. The const keyword is required in both the declaration and the definition. A constant member function cannot modify any data members or call any member functions that aren't constant.

// constant_member_function.cpp
class Date
{
public:
   Date( int mn, int dy, int yr );
   int getMonth() const;     // A read-only function
   void setMonth( int mn );   // A write function; can't be const
private:
   int month;
};

int Date::getMonth() const
{
   return month;        // Doesn't modify anything
}
void Date::setMonth( int mn )
{
   month = mn;          // Modifies data member
}
int main()
{
   Date MyDate( 7, 4, 1998 );
   const Date BirthDate( 1, 18, 1953 );
   MyDate.setMonth( 4 );    // Okay
   BirthDate.getMonth();    // Okay
   BirthDate.setMonth( 4 ); // C2662 Error
}