IO revisited

1. IO revisited

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

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

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: #include <stdio.h> #include <stdlib.h> int main() { int day, year; char weekday[20], month[20], dtm[100]; strcpy( dtm, "Saturday March 25 1989" ); sscanf( dtm, "%s %s %d %d", weekday, month, &day, &year ); printf("%s %d, %d = %s\n", month, day, year, weekday ); return(0); } Output: March 25, 1989 = Saturday

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)