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rand with vector of strings in a multimap


By : Queen
Date : July 31 2020, 12:00 PM
Hope this helps The right way of using rand() is to call srand() first. srand() will generate a series of random numbers, and rand() will simply iterate over them. If you don't call srand() you will get the same number every time you'll use 'rand()`.
srand example:
code :
int main() {
    // Call this function once to generate the random numbers using the seed `time(NULL)`
    srand(time(NULL));

    for (size_t i = 0; i < 10; i++) {
        std::cout << rand() % 5 << std::endl; // Go through the random numbers series
    }

    return EXIT_SUCCESS;
}
// Function to generate random numbers between `min` and `max` params
size_t get_random(size_t min, size_t max) {
    // the generator will only be seeded once since it's static (Equivalent to calling `srand` once)
    static std::mt19937 gen(std::random_device{}());
    std::uniform_int_distribution<size_t> dist(min, max);
    return dist(gen); // generate random number
}


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A cross between std::multimap and std::vector?


By : user2027552
Date : March 29 2020, 07:55 AM
Any of those help What you need is: Boost Multi-Index

Is this use of nested vector/multimap/map okay?


By : Muhammad Fahmi
Date : March 29 2020, 07:55 AM
Hope that helps To answer the headline question: yes, nesting STL containers is perfectly fine. Depending on your usage profile, this could result in excessive copying behind the scenes though. A better option might be to wrap the contents of all but top-level container using Boost::shared_ptr, so that container housekeeping does not require a deep copy of your nested container's entire contents. This would be the case say if you plan on spending a lot of time inserting and removing VecElem in the toplevel vector - expensive if VecElem is a direct multimap.
Memory overhead in the data structures is likely to be not significantly worse than anything you could design with equivalent functionality, and more likely better unless you plan to spend more time on this than is healthy.

How can I have two classes linked each other by a vector (map, multimap..) in C++?


By : user3168019
Date : March 29 2020, 07:55 AM
I wish this help you The simplest way is to forward declare or prototype all the classes and types in a common header, place guards on that, and include the header from all your code files. For example:
header.hpp:
code :
#ifndef COMMON_HPP
#define COMMON_HPP

class Corporation;
class Market;
class Equities;

typedef std::shared_ptr<Corporation> CorpRef;

typedef std::list<CorpRef> CorpList;

#endif /*COMMON_HPP*/
#include header.hpp

class Corporation
{
    static CorpRef Create();
};

A vector or multimap dilemma


By : Daniel Augusto Basto
Date : March 29 2020, 07:55 AM
seems to work fine If you want a multimap and not just a map, the alternative will probably be a vector< list > or something like that (actually a multimap is more or less a map with a list element type).
In general, a vector lookup is faster: it's O(1) for the array vs O(log n) for the map (in both case I'm not counting the search into the list/vector/set/whatever is used for the "multi" part). But, to use the vector, you have to make it as big as the biggest int key you want to use; if your keys are sequential this is not a problem, but if your index is sparse the multimap can be a better choice.

Convert multimap<Key,Value> to vector<vector<Value>>


By : Ayush
Date : March 29 2020, 07:55 AM
wish help you to fix your issue I need to convert an std::unordered_multimap to an std::vector>. I need to do this because my program will need to sort all the data, and maps can't be sorted. An example: , The usual multimap iteration should work here:
code :
std::vector<std::vector<T>> out;

for (auto it1 = m.begin(), it2 = it1, end = m.end(); it1 != end; it1 = it2)
{
    out.emplace_back();
    for ( ; it1->first == it2->first; ++it2)
    {
        out.back().push_back(it2->second);
    }
}
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