Question

I’ve got a prewritten function in C that fills an 1-D array with data, e.g.

int myFunction(myData **arr,...);


myData *array;
int arraySize;
arraySize = myFunction(&arr, ...);

I would like to call the function n times in a row with slightly different parameters (n is dependent on user input), and I need all the data collected in a single C array afterwards. The size of the returned array is not always fixed. Oh, and myFunction does the memory allocation internally. I want to do this in a memory-efficient way, but using realloc in each iteration does not sound like a good idea.

I do have all the C++ functionality available (the project is in C++, just using a C library), but using std::vector is no good because the collected data is later sent in to a function with a definition similar to:

void otherFunction(myData *data, int numData, ...);

Any ideas? Only things I can think of are realloc or using a std::vector and copying the data into an array afterwards, and those don’t sound too promising.

Answer 1

Just copy all of the data into an std::vector. You can call otherFunction on a vector v with

otherFunction(&v[0], v.size(), ...)

or

otherFunction(v.data(), v.size(), ...)

As for your efficiency requirement: it looks to me like your optimizing prematurely. First try this option, then measure how fast it is and only look for other solutions if it’s really too slow.