Most Boost libraries are header-only: they consist entirely of header files containing templates and inline functions, and require no separately-compiled library binaries or special treatment when linking.
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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
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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.
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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.cppclass 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 constprivate: 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}]]>