C ++ macro programming and macro Programming

C ++ macro programming and macro Programming
1. Define a macro function so that func (x) = X-1? In the simplest way, if x = 2, # define func (x) 1 is specially converted to x, so that # define func_helper_2 1 # define func (x) func_helper _ # x is created when x = 2. to promote to other numbers, you only need to define: # define func_helper_2 1 # define func_helper_3 2 # define func_helper_4 3... then we can get the decreasing and increasing functions # define DEC (X) # define INC (X)
2. How many macro variable parameters can be obtained? Take a look at this situation # define func (a1, a2, a3, a4,...) a4 what will happen if func (1, 2, 3, 4, 5) is passed in? Of course it is 4 to pass in func (x, 1, 2, 3, 4, 5) at this time? Is 3 passed to func (x, x, 1, 2, 3, 4, 5? Is 2 passed to func (x, 5? Is it 1? Is 1, 2, 3, so # define func2 (...) func (_ VA_ARGES _).
Finally, GET_ELEM_SIZE (X) is used to obtain the number of parameters in the 5-digit range.
3. Obtain the nth parameter? For example, GET_ELEMENT (a1, a2, a3), 2) expected to get a3?
# Define GET_ELEMENT (array, n) GET_ELEMENT _ # n arrayGET_ELEMENT_0 (e0,...) equals (e0, e1. ..) e1GET_ELEMENT_0 (e0, e1, e2...) e2
In this way, you can obtain the parameters of the specified coordinate position within three numbers.
4, int to BOOL? # Define INT_TO_BOOL (X) INT_TO_BOOL _ # X # define limit 0 # define limit 1 # define INT_TO_BOOL_2 1 # define INT_TO_BOOL_3 1 # define INT_TO_BOOL_4 1
5. IF branch? # Define IF_TEST (condition, true_verb, false_verb) IF_TEST _ # condition (true_verb, condition) \ # define condition (true_verb, false_verb) false_verb # define condition (true_verb, false_verb) true_verb
3, iterator? If ITER_FUNC (n, context) is defined as a macro function with n as the parameter, then: # define ITERATOR (n, ITER_FUNC, context) ITERATOR _ # n (ITER_FUNC, context) # define functions (n, func) # define ITERATOR_1 (func, context) ITERATOR_0 (func, context) func (1, context) # define ITERATOR_2 (func, context) ITERATOR_1 (func, context) func (2, context) # define ITERATOR_3 (func, context) ITERATOR_2 (func, context) func (3, context) reverse version # define ITERATOR_REVERSE (n, ITER_FUNC, context) ITERATOR_REVERSE _ # n (ITER_FUNC, context) # define functions (n, func) # define ITERATOR_REVERSE_1 (func, context) func (1, context) functions (func, context) # define functions (func, context) func (2, context) ITERATOR_REVERSE_1 (func, context) # define functions (func, context) func (3, context) ITERATOR_REVERSE_2 (func, context)
4. Data Structure? Based on the preceding tools, you can define the macro array structure. The array format can be defined as: array = (ele0, ele1, ele2) to obtain the array size, which can be used in Case 2: # define GET_ARRAY_SIZE (array) GET_ELEM_SIZE array accesses the array subscript to obtain the element: # define GET_ARRAY_ELEMENT (array, n) GET_ELEMENT (array, n) pushes an element: # define EXPAND_PARAM (param) param # define PUSH_ARRAY_ELEM (array, elem) EXPAND_PARAM array IF_TEST (GET_ARRAY_SIZE (array), EMPTY (), COMMA () elempop one element: # define POP_ARRAY_ELEM (array) ITERATOR (DEC (GET_ARRAY_SIZE (array), COPY_ARRAY_FROM, array) # define COPY_ARRAY_FROM (n, array) IF_TEST (n, EMPTY (), COMMA () GET_ARRAY_ELEMENT (array, n)

For example! What I catch up with is the implementation of c ++ tuple. Do you still remember the many tuple parameters? Review: \ file tuple. htemplate <> class tuple {}
Template <class T1> class tuple {tuple (T1 a1 ){}};
Template <class T1, class T2> class tuple {tuple (T1 a1, T2 ){}};
10 parameters are required to support 10 parameters...
Use macro iteration functions:
ITERATOR (2, GEN_TUPLE, pass)
# Define GEN_TUPLE (n, pass) \ template <ITERATOR (n, pass, GEN_TPARAM)> \ class tuple {\ tuple (ITERATOR (n, class T, GEN_PARAM )) {}\};
# Define GEN_TPARAM (n, pass) IF_TEST (n, EMPTY (), COMMA () class T # n # define GEN_PARAM (n, pass) IF_TEST (n, EMPTY (), COMMA () T # n a # n