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Validation

Validation. Buffering. C input is read from a buffer When the buffer is empty, Characters are moved into it For terminal, buffer is filled with a line For a file, buffer is filled with a disk “block” When no more data is available EOF (end-of-file) is indicated. getchar().

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Validation

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  1. Validation

  2. Buffering • C input is read from a buffer • When the buffer is empty, • Characters are moved into it • For terminal, buffer is filled with a line • For a file, buffer is filled with a disk “block” • When no more data is available • EOF (end-of-file) is indicated

  3. getchar() • Removes a character from the buffer • Refilling the buffer, if necessary • Returns the character as an integer • With EOF indicating end-of-file

  4. Robust programming • Make sure the input is valid • If something is wrong, • Give another chance • Handle end-of-file • And missing files • Don’t bomb

  5. Skipping to the end of line • Getting to a new line • Provides a good starting point while((ch=getchar()) && ch != ’\n’) process character while((ch=getchar()) && ch != ’\n’ && ch != EOF) process character

  6. Testing input with scanf() • scanf returns the number of items read • Be sure that it does! if (scanf(”%d”, &x) != 1) something is wrong • It might be better to • Only read one item per scanf • Skip to the end-of-line for a fresh start • And give a second chance at input

  7. Redirection • Unix and DOS allows terminal I/O from files • cprog < file.in • Standard input read from file.in • cprog > file.out • Standard output written to file.out

  8. End-of-file on terminal • On Unix • Type a Ctrl+D • The ASCII EOT (end of transmission) • On DOS and Windows • Type a Ctrl+Z • Descends from pre-Unix DEC operating systems • Stored as the last character of a file • Not a character read by the program

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