JNTU B.Tech III NETWORK PROGRAMMING Previous Question Paper (August - 2022 - R18)

The readn() and writen() functions are wrapper functions used to handle partial reads and writes in network programming, ensuring that the requested number of bytes is fully processed even if interrupted by signals or partial data availability.

These functions are necessary because the standard read() and write() system calls may return fewer bytes than requested if a signal interrupts the call or if the socket buffer is full/empty. readn() continues reading in a loop until exactly n bytes are read or an error/EOF occurs. Similarly, writen() ensures that all n bytes are written to the descriptor by repeatedly calling write() and updating the pointer and remaining count until the entire buffer is sent.

Byte manipulation functions are used to initialize, copy, or compare blocks of memory, which is essential when working with socket address structures like sockaddr_in.

• bzero(): Sets all bytes in a memory area to zero.
  void bzero(void *dest, size_t nbytes);
• bcopy(): Copies nbytes from source to destination. Note that the arguments are in the order (src, dest).
  void bcopy(const void *src, void *dest, size_t nbytes);
• bcmp(): Compares two memory areas for equality, returning 0 if identical.
  int bcmp(const void *ptr1, const void *ptr2, size_t nbytes);
• memset(): A more portable alternative to bzero(), setting n bytes of memory to a specific value c.
  void *memset(void *s, int c, size_t n);
• memcpy(): Similar to bcopy() but with standard C syntax (dest, src, n).
  void *memcpy(void *dest, const void *src, size_t n);
• memcmp(): Compares n bytes of two memory areas.
  int memcmp(const void *ptr1, const void *ptr2, size_t n);