How to read file contents as a character array in C using ifstream::read() and istreambuf_iterator?

How to Read File Contents as a Character Array in C

Background

This question asks how to populate a character array buffer with the bytes of a file named inputFile. The user has encountered difficulties with other suggested approaches that use getline() instead of ifstream::read().

Solution

There are a few approaches to address this task:

Using ifstream::read()

This method involves:

1. Opening the File: Use std::ifstream to open the file in binary mode to avoid character translations.
2. Determining File Size: Use seekg() and tellg() to obtain the file length.
3. Reading Data: Call read() to read the file contents into the buffer, ensuring the buffer size is sufficient.

Example Code:

<code class="cpp">// Open file in binary mode
std::ifstream infile("C:\MyFile.csv", std::ios_base::binary);

// Get file length
infile.seekg(0, std::ios::end);
size_t length = infile.tellg();
infile.seekg(0, std::ios::beg);

// Read file
infile.read(buffer, length);</code>

Using istreambuf_iterator

This approach is more modern and uses iterators to read the file:

1. Create an Istreambuf_iterator: Assign std::istreambuf_iterator(infile) to the begin iterator and std::istreambuf_iterator() to the end iterator.
2. Use Vector to Store Characters: Create a vector std::vector and push all characters from the begin to end iterator into the vector.
3. Copy Vector to Array: Assign the vector data to the buffer using std::copy.

Example Code:

<code class="cpp">// Create iterators
std::istreambuf_iterator<char> begin(infile);
std::istreambuf_iterator<char> end;

// Create vector
std::vector<char> contents(begin, end);

// Copy vector to array
std::copy(contents.begin(), contents.end(), buffer);</code>

Considerations

• File Size Limitations: ifstream::read() may overflow the buffer if the file size exceeds its size. Consider using buffered reads or resizable buffers instead.
• Error Handling: Check for potential read errors using infile.fail() or infile.eof() after read attempts.
• Binary Mode: If the file contains non-ASCII characters, open it in binary mode to preserve their original encoding.

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