Re: Converting between vectors

Victor Bazarov <v.bazarov@comcast.invalid>
Thu, 21 Apr 2011 11:59:11 -0400
On 4/21/2011 11:36 AM, Andrea Crotti wrote:

I need in short to serialize vector of different types into a stream of
chars, which is then sent over the network.
Boost unfortunately is not the answer since I can't use it in the

Until now I used the function below, but I found out that is terribly
buggy, since it doesn't work in all cases of type conversion and even

But I can't find a way to fix it and to make it general, any idea /hint?



template<typename INP, typename OUT>
std::vector<OUT> vectorConversion(const std::vector<INP>& input)
     size_t size_inp = sizeof(INP);
     size_t size_out = sizeof(OUT);
     // make sure the sizeof are multiples between them, otherwise it doesn't work!
     assert(((size_inp % size_out) == 0) || ((size_out % size_inp) == 0));
     std::vector<OUT> res;
     size_t size = (size_inp * input.size()) / size_out;
     // is it memcpy a good idea in this case?
     memcpy(&res[0],&input[0], size_inp * input.size());
     return res;

int main()
     std::vector<int> vec(5, 1);
     std::vector<long> lvec = vectorConversion<int, long>(vec);
     std::vector<int> vec2 = vectorConversion<long, int>(lvec);

     assert(vec == vec2);
     return 0;

First off, you should allow the compiler to detemine the 'INP' type from
the argument. Redefine your template as

    template<typename OUT, typename INP> ...

and use it this way:

    std::vector<long> lvec = vectorConversion<long>(vec);

then the argument you didn't explicitly provide will be deduced.

Second, 'memcpy' is not a good idea. A loop with assignment from one to
the other should do just fine.

Third, try plain initialization from a pair of iterators:

    std::vector<long> lvec(vec.begin(), vec.end());

I am not sure it should work if the value_type types are different, but
it costs next to nothing to try.

I do not respond to top-posted replies, please don't ask

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