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- DictionaryABC/ˌeɪbiːˈsiː/
noun
- 1. the alphabet: "millions of children every year learn how to say their ABC"
- 2. the rudiments of a subject: "the business had been learning the ABC of its trade"
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#define ABC 123 int n = ABC; would not compile. Now consider: #define ABC abc #pragma message "The value of ABC is: " ABC which is equivalent to. #pragma message "The value of ABC is: " abc This causes a preprocessor warning because abc (unquoted) cannot be concatenated with the preceding string.
Nov 17, 2017 · What does it mean in C : #define ABC(a,b) {#a, a, b} ? I understand that ABC is a Macro with parameters (a,b).
Since this question was originally asked, python has changed how abstract classes are implemented. I have used a slightly different approach using the abc.ABC formalism in python 3.6. Here I define the constant as a property which must be defined in each subclass.
See the abc module. Basically, you define __metaclass__ = abc.ABCMeta on the class, then decorate each abstract method with @abc.abstractmethod. Classes derived from this class cannot then be instantiated unless all abstract methods have been overridden.
Jun 2, 2015 · #define performs a token/textual replacement in the source code, not a semantic replacement. This screws up namespace use (#defined variables are replaced with values and not containing a fully qualified name). That is, given: namespace x { #define abc 1 } x::abc is an error, because the compiler actually tries to compile x::1 (which is invalid).
Jun 28, 2017 · from abc import ABCMeta class A(object): __metaclass__ = ABCMeta def __init__(self, n): self.n = n However, I do not want to let the A class be instantiated because, well, it is an abstract class. The problem is, this is actually allowed:
Oct 28, 2009 · you might try to "type" a #define ala #define S std::string("abc"), but the constant avoids repeated construction of distinct temporaries at each point of use; One Definition Rule complications; can take address, create const references to them etc. most similar to a non-const value, which minimises work and impact if switching between the two
Dec 18, 2020 · #define identifier token-sequence The preprocessor runs before the compiler transforms your code for use in the compiler. The order is as follows: Trigraph replacement; Line splicing; Macro definition and expansion; So with the #define you can have character manipulation (macro substitution). Whenever M is seen 4 will be substituted.
Feb 26, 2016 · The second #define ABC is invalid (unless the new definition is identical to the old one, which it isn't here). Some dodgy preprocessors might allow it; others will give warnings or errors. Some dodgy preprocessors might allow it; others will give warnings or errors.
Another possible solution is to use metaclasses.. A minimal example can look like this: class BaseMetaClass(type): def __new__(mcls, class_name, bases, attrs): required_attrs = ('foo', 'bar') for attr in required_attrs: if attr not in attrs: raise RuntimeError(f"You need to set {attr} in {class_name}") return super().__new__(mcls, class_name, bases, attrs) class Base(metaclass=BaseMeta): foo: str bar: int
