Sorting a vector of objects in C++

Question

struct Keyword
{
    std::string keyword;
    int numUses;
};  

bool sortingVector(const Keyword& key1, const Keyword& key2)
{
    return key1.numUses < key2         


        

Answer 1

Put std:: in front of your sort call. And #include <algorithm> at the top of the source file.

Answer 2

are you using namespace std; ? if not you want std::sort()

Answer 3

You probably want to call std::sort instead of plain sort and might have to include the appropriate header file (algorithmunless I'm mistaken).

Answer 4

This is what a compilable example should look like:

Because you did not provide the exact code that was generating the errors people have given a couple of different types of answer. As a result it is generally a good idea to generate a compilable example the displays the problem.

#include <algorithm>
#include <vector>
#include <string>

struct Keyword
{
        std::string keyword;
            int numUses;
};

bool sortingVector(const Keyword& key1, const Keyword& key2)
{
        return key1.numUses < key2.numUses;
}

int main()
{
    std::vector<Keyword>    topKeywords;

    std::sort(topKeywords.begin(), topKeywords.end(), sortingVector);
}

Generally the compiler can do a better job of optimising (I am told) if you use a functor rather than a function pointer.

struct SortingVectorFunctor
{
    bool operator()(const Keyword& key1, const Keyword& key2) const
    {
        return key1.numUses < key2.numUses;
    }
};

Answer 5

#include <vector>
#include <algorithm>
#include <string>

struct Keyword
{
    std::string keyword;
    int numUses;
};  

bool sortingVector(const Keyword& key1, const Keyword& key2)
{
    return key1.numUses < key2.numUses;
}

int main()
{
    std::vector<Keyword> topKeywords(100);

    // imagine topKeywords initialization here

    std::sort(topKeywords.begin(), topKeywords.end(), sortingVector);

    return 0;
}

Compiles fine on my machine (gcc version 4.4.3).

Answer 6

Is sortingVector a non-static member of some class? The error message suggests that it is, in which case you will need to wrap it (using boost::bind, for example) into a binary operation that doesn't take a this parameter. You might want to make sortingVector a static member or a free function instead.