Read and write bytes from a file (c++)

Question

I think I probably have to use an fstream object but i'm not sure how. Essentially I want to read in a file into a byte buffer, modify it, then rewrite these bytes to a file. So I just need to know how to do byte i/o. Thanks

Answer 1

#include <fstream>
std::ifstream fileBufferHere(inputFileName, std::ios::in|std::ios::binary);;
std::ofstream outputBufferHere(outputFilename, std::ios::binary|std::ios::out);
char *m_content = new char[1024];

if(fileBufferHere.is_open())
{
    fileBufferHere.seekg(0, std::ios::beg);
    fileBufferHere.getline(m_content, 1024);
}

/*MODIFY HERE*/

outputBufferHer.write(content, sizeof(content));

outputBufferHere.close();
fileBufferHer.close();

From memory i think this is how it goes...

Answer 2

While doing file I/O, you will have to read the file in a loop checking for end of file and error conditions. You can use the above code like this

while (fileBufferHere.good()) {  
    filebufferHere.getline(m_content, 1024)  
    /* Do your work */  
}

Answer 3

If you are dealing with a small file size, I recommend that reading the whole file is easier. Then work with the buffer and write the whole block out again. These show you how to read the block - assuming you fill in the open input/output file from above reply

  // open the file stream
  .....
  // use seek to find the length, the you can create a buffer of that size
  input.seekg (0, ios::end);   
  int length = input.tellg();  
  input.seekg (0, ios::beg);
  buffer = new char [length];
  input.read (buffer,length);

  // do something with the buffer here
  ............
  // write it back out, assuming you now have allocated a new buffer
  output.write(newBuffer, sizeof(newBuffer));
  delete buffer;
  delete newBuffer;
  // close the file
  ..........