geotavros geotavros - 1 year ago 53
C++ Question

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

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 Source

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.