finally.c.ppt
- 2. Chapter 8 File management in C 2 Profesor: Edwin o. omandi
- 3. Console oriented Input/Output • Console oriented – use terminal (keyboard/screen) • scanf(“%d”,&i) – read data from keyboard • printf(“%d”,i) – print data to monitor • Suitable for small volumes of data • Data lost when program terminated
- 4. Real-life applications • Large data volumes • Example: physical experiments (CERN collider), human genome, population records etc. • Need for flexible approach to store/retrieve data • Concept of files
- 5. Files • File – place on disc where group of related data is stored – E.g. your C programs, executables • High-level programming languages support file operations – Naming – Opening – Reading – Writing – Closing
- 6. Defining and opening file • To store data file in secondary memory (disc) must specify to OS – Filename (e.g. sort.c, input.data) – Data structure (e.g. FILE) – Purpose (e.g. reading, writing, appending)
- 7. Filename • String of characters that make up a valid filename for OS • May contain two parts – Primary – Optional period with extension • Examples: a.out, prog.c, temp, text.out
- 8. General format for opening file • fp – contains all information about file – Communication link between system and program • Mode can be – r open file for reading only – w open file for writing only – a open file for appending (adding) data FILE *fp; /*variable fp is pointer to type FILE*/ fp = fopen(“filename”, “mode”); /*opens file with name filename , assigns identifier to fp */
- 9. Different modes • Writing mode – if file already exists then contents are deleted, – else new file with specified name created • Appending mode – if file already exists then file opened with contents safe – else new file created • Reading mode – if file already exists then opened with contents safe – else error occurs. FILE *p1, *p2; p1 = fopen(“data”,”r”); p2= fopen(“results”, w”);
- 10. Additional modes • r+ open to beginning for both reading/writing • w+ same as w except both for reading and writing • a+ same as ‘a’ except both for reading and writing
- 11. Closing a file • File must be closed as soon as all operations on it completed • Ensures – All outstanding information associated with file flushed out from buffers – All links to file broken – Accidental misuse of file prevented • If want to change mode of file, then first close and open again
- 12. Closing a file • pointer can be reused after closing Syntax: fclose(file_pointer); Example: FILE *p1, *p2; p1 = fopen(“INPUT.txt”, “r”); p2 =fopen(“OUTPUT.txt”, “w”); …….. …….. fclose(p1); fclose(p2);
- 13. Input/Output operations on files • C provides several different functions for reading/writing • getc() – read a character • putc() – write a character • fprintf() – write set of data values • fscanf() – read set of data values • getw() – read integer • putw() – write integer
- 14. Errors that occur during I/O • Typical errors that occur – trying to read beyond end-of-file – trying to use a file that has not been opened – perform operation on file not permitted by ‘fopen’ mode – open file with invalid filename – write to write-protected file
- 15. THANK YOU