How to cheaply assign C-style array to std::vector?

c++ arrays stl vector stdvector
Dmitriy picture Dmitriy · Apr 29, 2011 · Viewed 13.1k times · Source

Currently I do the following:

// float *c_array = new float[1024];

void Foo::foo(float *c_array, size_t c_array_size) {
  //std::vector<float> cpp_array;

  cpp_array.assign(c_array, c_array + c_array_size);
  delete [] c_array;
}

How can I optimize this assigning? I would like not to perform elementwise copy but just swap pointers.

Answer

Mark B picture Mark B · Apr 29, 2011

The current std::vector doesn't provide any capability or interface to take ownership of previously allocated storage. Presumably it would be too easy to pass a stack address in by accident, allowing more problems than it solved.

If you want to avoid copying into a vector, you'll either need to use vectors through your entire call chain, or do it the C way with float[] the entire time. You can't mix them. You can guaranteed that &vec[0] will be equivalent to the C-array though, fully contiguous, so using vector in the whole program may be feasible.

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