How to Optimize Reading Binary Files into a Vector of Unsigned Chars?

Binary File Reading Optimization

To optimally read binary files into a vector of unsigned chars, consider the following strategies:

Method 1: Custom Vector Construction

<code class="cpp">std::vector<BYTE> readFile(const char* filename)
{
    std::ifstream file(filename, std::ios::binary);
    std::streampos fileSize = file.tellg();
    file.seekg(0, std::ios::beg);
    std::vector<BYTE> fileData(fileSize);
    file.read((char*) &fileData[0], fileSize);
    return fileData;
}</code>

This method explicitly creates a vector with the correct size based on file size. However, it casts the vector's data to char*, which is undesirable.

Method 2: Istreambuf Iterator

<code class="cpp">std::vector<BYTE> readFile(const char* filename)
{
    std::ifstream file(filename, std::ios::binary);
    return std::vector<BYTE>((std::istreambuf_iterator<char>(file)),
                              std::istreambuf_iterator<char>());
}</code>

This method uses an iterator that reads data into a char buffer internally. Although it is shorter, it still requires char iterators despite reading unsigned chars.

Method 3: Basic Ifstream Specialization

<code class="cpp">std::vector<BYTE> readFile(const char* filename)
{
    std::basic_ifstream<BYTE> file(filename, std::ios::binary);
    return std::vector<BYTE>((std::istreambuf_iterator<BYTE>(file)),
                              std::istreambuf_iterator<BYTE>());
}</code>

This method uses a specialized input file stream for unsigned chars. However, it may not be appropriate for all cases.

Optimizations

• Reserve Capacity: Preallocating memory for the vector improves performance.
• Disable Newline Suppression: ios::skipws in binary mode can cause performance issues; disable it with unsetf.
• istream_iterator vs. std::copy: std::copy may avoid overhead associated with operator >>.

Considerations

• Istreambuf iterators may be preferred for their simplicity, but custom iterators may offer better performance.
• The "best" method depends on the specific requirements of the application and the data being read.

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