Read/Write

Objectives

1. Understand the read and write system calls.

Notes

• ssize_t read(int fd, void * buffer, size_t count);
• ssize_t write(int fd, const void * buffer, size_t count);
• Both:
  • require unistd.h
  • Take the correct type of open file descriptor.
  • Take a buffer, the data to read/write
  • Take a size, the number bytes to read/write
  • Return the actual number of bytes read/written
    • This may be less than the requested amount
    • Lack of data to read
    • Lack of space/resource to write.
  • Return -1 on error
• THESE FUNCTIONS DEAL WITH RAW I/O
  • Whatever BYTES are in the buffer/file will be transferred
  • This is opposed to << , >> or getline in c++ where the bytes will be converted to ascii then written.
• int close(int fd);
  • Close the file.
  • If the file was removed in any way, when the last open file descriptor is closed, the file is destroyed.
  • returns
    • 0 on success
    • -1 on error.