1. Console and File I/O - Basics Rudra Dutta CSC 230 - Spring 2007, Section 001

2. Copyright Rudra Dutta, NCSU, Spring, 20072 Input and Output User interaction: reading and writing data – Reading from keyboard or file – Writing to console or file C provides NO language primitives for I/O ! – Library functions provide mechanisms – Standard libraries Complex functions build on simple ones, but… What do simple functions build on? – Direct interaction with OS – “System” functions, provided as library

3. Copyright Rudra Dutta, NCSU, Spring, 20073 Character I/O Standard library treats all I/O as occurring in text streams int getchar() – Reads single next character from the input stream represented by the keyboard – Returns as … int !! int putchar(int c) – Takes the single character c (passed as int !) – Prints it on the output stream which is the console

4. Copyright Rudra Dutta, NCSU, Spring, 20074 Copy Input to Output #include int main() { int c; while ((c = getchar ()) != EOF) { putchar (c); }

5. Copyright Rudra Dutta, NCSU, Spring, 20075 Files General meaning - not console or keyboard, but something on disk Console and keyboard can be seen as special cases – Then all stream input and output can be represented as files Three special files – stdin - keyboard – stdout - default display, console – stderr - usually also default display, logically different Functions actually defined on files – File versions: fgetc(), fputc() – See manual pages for getchar() and putchar() On keyboard, what is End Of File? – A Ctl-D can by typed to indicate EOF

6. Copyright Rudra Dutta, NCSU, Spring, 20076 Shell Redirections Input or output of a program can be redirected from the command line –, | Meaning of redirecting input: – “Provide the program to be run with the contents of this file as if it is coming from stdin” – Similar meaning in redirecting output Piping – “Run both these programs, piping the stdout of the first one into the stdin of the second one”

7. Copyright Rudra Dutta, NCSU, Spring, 20077 Using Text Files stdio.h contains a structure called FILE – Can be used by thinking of it as a type – Indicates a stream Can be opened by fopen(), closed by fclose() – All opened files effectively close when program terminates (usually, this is an OS and not C issue) – But leaving out an fclose() can cause many errors and subsequent headaches Opening a file returns a file pointer – Like a handle, but actually a pointer in the C sense – Must be used to read/write/close

8. Copyright Rudra Dutta, NCSU, Spring, 20078 Formatted I/O printf() and scanf() – Exclusively for stdout and stdin, respectively Consider printf() – Allows programmer to pass a “format string”, and indicate placeholders – Remaining arguments specify values to use for placeholders – Variable number of argument ! scanf() – Also uses format string – Must pass locations of variables whose values will be read into – Use of pointers - we shall revisit appropriately Using text files – fprintf() and fscanf() – Exactly the same, except addition first argument is file pointer

9. Copyright Rudra Dutta, NCSU, Spring, 20079 printf() Conversions Format string needs its own “language” to specify types of variable values – Why? Name of variable indicates only location where variable can be found – Does not indicate type – Therefore, how many bytes it occupies Coversions are listed in manual pages – More accesibly, in text