How to Efficiently Load a File into an `std::vector`?

Efficiently Loading a File into an std::vector

To efficiently load a file into an std::vector, one must avoid unnecessary copies and memory reallocations. While the original approach utilizing reserve and read() may seem direct, reserve() alone does not alter the vector's capacity.

Canonical Method Using Iterators:

The canonical approach employs input stream iterators to conveniently construct the vector from the file contents:

#include <iterator>
// ...

std::ifstream testFile("testfile", std::ios::binary);
std::vector<char> fileContents((std::istreambuf_iterator<char>(testFile)),
                               std::istreambuf_iterator<char>());

Optimizing for Reallocations:

If minimizing memory reallocations is crucial, allocate space in the vector before loading the file contents:

#include <iterator>
// ...

std::ifstream testFile("testfile", std::ios::binary);
std::vector<char> fileContents;
fileContents.reserve(fileSize);
fileContents.assign(std::istreambuf_iterator<char>(testFile),
                    std::istreambuf_iterator<char>());

By utilizing stream iterators and pre-allocating memory when necessary, these approaches offer efficient file loading into an std::vector.

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