How to initialise data concisely in C++

In the past, creating a collection of dates was a chore, because you had to individually insert them into a container (e.g. declaring a vector on one line and then pushing dates into it on subsequent lines). With features like std::initializer_list from C++11 onwards, it’s now much easier to do this concisely.

Here’s some simple, concise code to create dates without all the hassle:

struct Date
{
    std::string Event;

    int Year;
    int Month;
    int Day;
};

void print( const Date& date )
{
    std::cout << date.Event << ": "<< date.Year << "/" << date.Month << "/" << date.Day << "\n";
}

void print( const std::vector<Date>& dates )
{
    for ( auto date : dates )
    {
        print( date );
    }
}

void test()
{
    std::cout << "Print date:\n";
    print( { "Today", 2015, 5, 5 } );

    std::cout << "Print dates:\n";
    print( {
        { "Christmas", 2015, 12, 25 },
        { "Spring Bank Holiday", 2016, 6, 30 }
           } );
}

This style is particularly useful when writing tests – you can write a whole test, including setting up the data, on a single line (or at least, in a single function call).

Another compelling use case comes when creating test cases for graph algorithms. Suppose you have the following data structures for an undirected, weighted graph:

struct Edge
{
    const size_t end1;
    const size_t end2;
    const size_t cost;
};

struct Graph
{
    size_t source;
    size_t nodes;
    std::vector<Edge> edges;
};

Then creating a test graph to pass into an algorithm is as simple as:

shortest_path( { 0, 4, { {0,1,24}, {0,3,20}, {2,0,3}, {3,2,12} } })

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Filed under C++, C++ Code, Programming

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