IO revisited

1. IO revisited CSE 2451 Rong Shi

2. stdio.h • Functions • printf • scanf (normally stops at whitespace) • fgets • sscanf • Standard streams • stdin (defaults to keyboard) • stdout (defaults to console) • stderr (defaults to console)

3. scanf and incorrect input • scanf input is based on pattern matching • If incorrect input is entered, the pattern is not matched and the input characters remain in the buffer • See scanftest.c

4. fgets – get string from stream • char *fgets(char *s, int size, FILE *stream); • Read in size - 1 characters from the stream and stores it into *s pointer. • The string is automatically null-terminated. • fgets stops reading in characters if it reaches an EOF or newline. • Ex: char s[100]; fgets(s, sizeof(s), stdin); // read a line from stdin • Use sscanf to process the string

5. sscanf– read formatted data from string • intsscanf(const char *str, const char *format, ...); • *str is a string / character array / pointer to character • *format is a string literal • Additional arguments are pointers to the types in *format • Ex: inti; char s[100]; fgets(s, sizeof(s), stdin); // read a line from stdin sscanf(s,"%d", &i);

6. IO redirection • When running an executable > redirects output < redirects input | pipe (stdout from one program to stdinof another) Examples: testprog > fileout (output of testprog goes to fileout) testprog < filein (input of testprog comes from filein) prog1 | prog2 (input of prog2 comes from output of prog1)