#include <wx/datetime.h>
This class is a "logical time span" and is useful for implementing program logic for such things as "add one month to the date" which, in general, doesn't mean to add 60*60*24*31 seconds to it, but to take the same date the next month (to understand that this is indeed different consider adding one month to Feb, 15 – we want to get Mar, 15, of course).
When adding a month to the date, all lesser components (days, hours, ...) won't be changed unless the resulting date would be invalid: for example, Jan 31 + 1 month will be Feb 28, not (nonexisting) Feb 31.
Because of this feature, adding and subtracting back again the same wxDateSpan will not, in general, give back the original date: Feb 28  1 month will be Jan 28, not Jan 31!
wxDateSpan objects can be either positive or negative. They may be multiplied by scalars which multiply all deltas by the scalar: i.e. 2*(1 month and 1 day) is 2 months and 2 days. They can be added together with wxDateTime or wxTimeSpan, but the type of result is different for each case.
Equality operators are defined for wxDateSpans. Two wxDateSpans are equal if and only if they both give the same target date when added to every source date. Thus wxDateSpan::Months(1) is not equal to wxDateSpan::Days(30), because they don't give the same date when added to Feb 1st. But wxDateSpan::Days(14) is equal to wxDateSpan::Weeks(2).
Finally, notice that for adding hours, minutes and so on you don't need this class at all: wxTimeSpan will do the job because there are no subtleties associated with those (we don't support leap seconds).
Public Member Functions  
wxDateSpan (int years=0, int months=0, int weeks=0, int days=0)  
Constructs the date span object for the given number of years, months, weeks and days. More...  
wxDateSpan  Add (const wxDateSpan &other) const 
Returns the sum of two date spans. More...  
wxDateSpan &  Add (const wxDateSpan &other) 
Adds the given wxDateSpan to this wxDateSpan and returns a reference to itself. More...  
int  GetDays () const 
Returns the number of days (not counting the weeks component) in this date span. More...  
int  GetMonths () const 
Returns the number of the months (not counting the years) in this date span. More...  
int  GetTotalMonths () const 
Returns the combined number of months in this date span, counting both years and months. More...  
int  GetTotalDays () const 
Returns the combined number of days in this date span, counting both weeks and days. More...  
int  GetWeeks () const 
Returns the number of weeks in this date span. More...  
int  GetYears () const 
Returns the number of years in this date span. More...  
wxDateSpan  Multiply (int factor) const 
Returns the product of the date span by the specified factor. More...  
wxDateSpan &  Multiply (int factor) 
Multiplies this date span by the specified factor. More...  
wxDateSpan &  Neg () 
Changes the sign of this date span. More...  
wxDateSpan  Negate () const 
Returns a date span with the opposite sign. More...  
wxDateSpan &  SetDays (int n) 
Sets the number of days (without modifying any other components) in this date span. More...  
wxDateSpan &  SetMonths (int n) 
Sets the number of months (without modifying any other components) in this date span. More...  
wxDateSpan &  SetWeeks (int n) 
Sets the number of weeks (without modifying any other components) in this date span. More...  
wxDateSpan &  SetYears (int n) 
Sets the number of years (without modifying any other components) in this date span. More...  
wxDateSpan  Subtract (const wxDateSpan &other) const 
Returns the difference of two date spans. More...  
wxDateSpan &  Subtract (const wxDateSpan &other) 
Subtracts the given wxDateSpan to this wxDateSpan and returns a reference to itself. More...  
wxDateSpan &  operator+= (const wxDateSpan &other) 
Adds the given wxDateSpan to this wxDateSpan and returns the result. More...  
wxDateSpan &  operator= (const wxDateSpan &other) 
Subtracts the given wxDateSpan to this wxDateSpan and returns the result. More...  
wxDateSpan &  operator () 
Changes the sign of this date span. More...  
wxDateSpan &  operator*= (int factor) 
Multiplies this date span by the specified factor. More...  
bool  operator!= (const wxDateSpan &other) const 
Returns true if this date span is different from the other one. More...  
bool  operator== (const wxDateSpan &other) const 
Returns true if this date span is equal to the other one. More...  
Static Public Member Functions  
static wxDateSpan  Day () 
Returns a date span object corresponding to one day. More...  
static wxDateSpan  Days (int days) 
Returns a date span object corresponding to the given number of days. More...  
static wxDateSpan  Month () 
Returns a date span object corresponding to one month. More...  
static wxDateSpan  Months (int mon) 
Returns a date span object corresponding to the given number of months. More...  
static wxDateSpan  Week () 
Returns a date span object corresponding to one week. More...  
static wxDateSpan  Weeks (int weeks) 
Returns a date span object corresponding to the given number of weeks. More...  
static wxDateSpan  Year () 
Returns a date span object corresponding to one year. More...  
static wxDateSpan  Years (int years) 
Returns a date span object corresponding to the given number of years. More...  
wxDateSpan::wxDateSpan  (  int  years = 0 , 
int  months = 0 , 

int  weeks = 0 , 

int  days = 0 

) 
Constructs the date span object for the given number of years, months, weeks and days.
Note that the weeks and days add together if both are given.
wxDateSpan& wxDateSpan::Add  (  const wxDateSpan &  other  ) 
Adds the given wxDateSpan to this wxDateSpan and returns a reference to itself.
wxDateSpan wxDateSpan::Add  (  const wxDateSpan &  other  )  const 
Returns the sum of two date spans.

static 
Returns a date span object corresponding to one day.

static 
Returns a date span object corresponding to the given number of days.
int wxDateSpan::GetDays  (  )  const 
Returns the number of days (not counting the weeks component) in this date span.
int wxDateSpan::GetMonths  (  )  const 
Returns the number of the months (not counting the years) in this date span.
int wxDateSpan::GetTotalDays  (  )  const 
Returns the combined number of days in this date span, counting both weeks and days.
This doesn't take months or years into account.
int wxDateSpan::GetTotalMonths  (  )  const 
Returns the combined number of months in this date span, counting both years and months.
int wxDateSpan::GetWeeks  (  )  const 
Returns the number of weeks in this date span.
int wxDateSpan::GetYears  (  )  const 
Returns the number of years in this date span.

static 
Returns a date span object corresponding to one month.

static 
Returns a date span object corresponding to the given number of months.
wxDateSpan& wxDateSpan::Multiply  (  int  factor  ) 
Multiplies this date span by the specified factor.
The product is computed by multiplying each of the components by the factor.
wxDateSpan wxDateSpan::Multiply  (  int  factor  )  const 
Returns the product of the date span by the specified factor.
The product is computed by multiplying each of the components by the factor.
wxDateSpan& wxDateSpan::Neg  (  ) 
Changes the sign of this date span.
wxDateSpan wxDateSpan::Negate  (  )  const 
Returns a date span with the opposite sign.
bool wxDateSpan::operator!=  (  const wxDateSpan &  other  )  const 
Returns true if this date span is different from the other one.
wxDateSpan& wxDateSpan::operator*=  (  int  factor  ) 
Multiplies this date span by the specified factor.
The product is computed by multiplying each of the components by the factor.
wxDateSpan& wxDateSpan::operator+=  (  const wxDateSpan &  other  ) 
Adds the given wxDateSpan to this wxDateSpan and returns the result.
wxDateSpan& wxDateSpan::operator  (  ) 
Changes the sign of this date span.
wxDateSpan& wxDateSpan::operator=  (  const wxDateSpan &  other  ) 
Subtracts the given wxDateSpan to this wxDateSpan and returns the result.
bool wxDateSpan::operator==  (  const wxDateSpan &  other  )  const 
Returns true if this date span is equal to the other one.
Two date spans are considered equal if and only if they have the same number of years and months and the same total number of days (counting both days and weeks).
wxDateSpan& wxDateSpan::SetDays  (  int  n  ) 
Sets the number of days (without modifying any other components) in this date span.
wxDateSpan& wxDateSpan::SetMonths  (  int  n  ) 
Sets the number of months (without modifying any other components) in this date span.
wxDateSpan& wxDateSpan::SetWeeks  (  int  n  ) 
Sets the number of weeks (without modifying any other components) in this date span.
wxDateSpan& wxDateSpan::SetYears  (  int  n  ) 
Sets the number of years (without modifying any other components) in this date span.
wxDateSpan& wxDateSpan::Subtract  (  const wxDateSpan &  other  ) 
Subtracts the given wxDateSpan to this wxDateSpan and returns a reference to itself.
wxDateSpan wxDateSpan::Subtract  (  const wxDateSpan &  other  )  const 
Returns the difference of two date spans.

static 
Returns a date span object corresponding to one week.

static 
Returns a date span object corresponding to the given number of weeks.

static 
Returns a date span object corresponding to one year.

static 
Returns a date span object corresponding to the given number of years.