Reading binary file in C (in chunks)

Question

I'm not good at C and I'm trying to do something simple. I want to open a binary file, read blocks of 1024 bytes of data and dump into a buffer, process the buffer, read another 1024 byes of data and keep doing this until EOF. I know how / what I want to do with the buffer, but it's the loop part and file I/O I keep getting stuck on.

PSEUDO code:

FILE *file;
unsigned char * buffer[1024];

fopen(myfile, "rb");

while (!EOF)
{
  fread(buffer, 1024);
  //do my processing with buffer;
  //read next 1024 bytes in file, etc.... until end
}

while (!EOF) { ...} EOF is a constant. Note: fread() takes 4 arguments. And it returns a value. — wildplasser
@wildplasser I think this is the unfortunately chosen "PSEUDOCODE" part. Not sure though. — luk32

Paul Roub Paul Roub · Accepted Answer · 2015-01-28T16:46:27

fread() returns the number of bytes read. You can loop until that's 0.

FILE *file = NULL;
unsigned char buffer[1024];  // array of bytes, not pointers-to-bytes
size_t bytesRead = 0;

file = fopen(myfile, "rb");   

if (file != NULL)    
{
  // read up to sizeof(buffer) bytes
  while ((bytesRead = fread(buffer, 1, sizeof(buffer), file)) > 0)
  {
    // process bytesRead worth of data in buffer
  }
}

Reading binary file in C (in chunks)

1 Answers