How to Efficiently Read a File into a `std::vector` Without Overhead?

Efficient File Handling into a Character Vector

In a quest to optimize file reading into an std::vector, a developer encounters a challenge. The typical method using reserve and subsequent read leads to an error due to the lack of elements at index 0. Other methods such as resize or initializing a vector with a size incur an overhead that the developer wishes to avoid.

The solution lies in the use of iterators. By creating an input streambuf iterator and using it to construct a vector, the file's contents can be directly assigned to the vector without the need for intermediate copies. The following code snippet illustrates this approach:

#include<iterator>

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

For performance concerns, reserving space in the vector prior to assignment can prevent reallocations:

std::vector<char> fileContents;
fileContents.reserve(fileSize);
fileContents.assign(std::istreambuf_iterator<char>(testFile),
                    std::istreambuf_iterator<char>());

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