File and Network I O CS 2022 Introduction to C Instructor Hussam Abu Libdeh Cornell University based on slides by Saikat Guha Fall 2011 Lecture 8 File and Network I O CS 2022 Fall 2011 Lecture 8 Input and Output I I I Keyboard I O Disk I O Network I O File and Network I O CS 2022 Fall 2011 Lecture 8 Streams I I I In many programming languages input output are done in streams Data exists on the stream you consume part of it and move on Examples I I I I I stdout standard output stream stderr standard error output stream stdin standard input stream files network sockets network connections File and Network I O CS 2022 Fall 2011 Lecture 8 Output to Terminal I Write a line to stdout I I Write a formatted line to stdout I I puts hello world printf Borat says Hi s n i Can write to streams other than stdout I fputs an error message stderr fprintf stderr Error on value d n i File and Network I O CS 2022 Fall 2011 Lecture 8 Input from User Keyboard Reading till end of line char buf 128 fgets buf 128 stdin Reading formatted input int i j char buf 128 scanf d d s i j buf File and Network I O CS 2022 Fall 2011 Lecture 8 File I O The C standard library way I I Use fopen fclose Deals with streams The POSIX way I I Use open close Deals with file descriptors We will only discuss POSIX I O here To read more about C streams check out the man pages and or http www cs cf ac uk Dave C CE html File and Network I O CS 2022 Fall 2011 Lecture 8 File I O Opening and closing files int fd File Descriptor fd open path to file O RDWR O CREAT close fd Reading and Writing char buf 4096 int len len read fd buf 4096 len write fd buf 4096 WARNING Size passed is only a suggestion May read write fewer than requested number of bytes Return value is number of bytes actually read written MUST retry if not fully read written File and Network I O CS 2022 Fall 2011 Lecture 8 File I O I I I I I I lseek fd numbytes SEEK CUR Seek numbytes from from current location sync Ensure bytes hit the disk Not needed for the most part FILE ffd fdopen fd r Construct a stream from file descriptor fprintf ffd format args Write formatted text output to file fscanf ffd format args Read formatted input from the file fclose ffd Close a stream File and Network I O CS 2022 Fall 2011 Lecture 8 Network I O Opening and closing network sockets int sock File Descriptor sock socket PF INET SOCK STREAM IPPROTO TCP close sock Internet Addresses struct sockaddr in addr addr sin family AF INET addr sin addr s addr htonl 0x7F000001 addr sin port htons 8080 Fill the address info manually or get the info automatically with getaddrinfo See man getaddrinfo File and Network I O CS 2022 Fall 2011 Lecture 8 Network I O Server srv socket PF INET SOCK STREAM IPPROTO TCP err bind srv struct sockaddr addr sizeof addr if err err listen srv 5 if err cli accept srv NULL 0 Client cli socket PF INET SOCK STREAM IPPROTO TCP err connect cli struct sockaddr addr sizeof addr if err Read Write data just as you would with file descriptors File and Network I O CS 2022 Fall 2011 Lecture 8 Very Helpful Resources Network Programming Beej s guide to network programming http beej us guide bgnet General C Programming Dave s programming C tutorials http www cs cf ac uk Dave C CE html File and Network I O CS 2022 Fall 2011 Lecture 8