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  1. #include <iostream>
  2. #include <vector>
  3. #include <string>
  4. using namespace std;
  5.  
  6. //================================================================
  7.  
  8. #define SumValuesFrom(container, member) priv_XValuesFrom_normal(container, member, [](const decltype(container.front().member) &valueA, const decltype(container.front().member) &valueB) { return (valueA + valueB); })
  9. #define SumValuesFromPtr(container, member) priv_XValuesFrom_ptr(container, member, [](const decltype(container.front()->member) &valueA, const decltype(container.front()->member) &valueB) { return (valueA + valueB); })
  10.  
  11. #define priv_XValuesFrom_normal(container, member, addingFunctor) priv_XValuesFrom<decltype(container.front().member)>(container, [](const decltype(container)::value_type &element) { return element.member; }, addingFunctor)
  12. #define priv_XValuesFrom_ptr(container, member, addingFunctor)    priv_XValuesFrom<decltype(container.front().member)>(container, [](const decltype(container)::value_type &element) { return element->member; }, addingFunctor)
  13.  
  14. template<typename ValueType, typename ContainerType, typename ReadingFunctor, typename AddingFunctor>
  15. ValueType priv_XValuesFrom(const ContainerType &container, ReadingFunctor getValue, AddingFunctor addValues, ValueType initialValue = ValueType())
  16. {
  17. 	ValueType total = initialValue;
  18.  
  19. 	for(const auto &element : container)
  20. 	{
  21. 		total = addValues(total, getValue(element));
  22. 	}
  23.  
  24. 	return total;
  25. }
  26.  
  27. //================================================================
  28.  
  29. struct MyStruct
  30. {
  31. 	MyStruct(int value) : memberVariable(value) { }
  32.  
  33. 	std::string otherData = "";
  34. 	int memberVariable = 1;
  35. };
  36.  
  37. int main()
  38. {
  39. 	std::vector<MyStruct> myContainer = {{1},{2},{3},{4}};
  40.  
  41. 	//Sum and display the values of *a member variable* within each element of a container.
  42. 	std::cout << "Total is: " << SumValuesFrom(myContainer, memberVariable) << std::endl;
  43.  
  44. 	return 0;
  45. }
Success #stdin #stdout 0s 3428KB
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Standard input is empty
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Total is: 10
https://ideone.com/Ww09qr
Testing a macro that can add up member-variables from elements of a container.
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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