EOF & Fseek Gustavo Olmeta Cindy Gonzalez Ana Arias Jeffrey Barajas Frank Rodriguez

1. EOF & FseekGustavo OlmetaCindy Gonzalez Ana AriasJeffrey Barajas Frank Rodriguez

2. EOF program Detecting end of file

3. Definition feof(): is used to determine whether the end-of-file indicator is set for the file associated to stdin. Returns a nonzero value if it is. It’s often used as a condition in a while loop to keep the program reading the file until the end-of-file indicator is reached. Function prototype: intfeof(FILE *fptr)

4. Purpose The End of File program opens, reads and displays a user specified text file line by line until the end of file indicator is reached.

5. Outline and Flowchart • Create Variables • #define BUFSIZE 100 • char buf[BUFSIZE] • char filename[20] • FILE *fp • User interface • puts(“Enter name of text file to display:”) • gets(filename) • Open file • fp = fopen(filename, “r”)) == NULL) • Read and display until EOF • while (!feof(fp)) {fgets(buf, BUFSIZE, fp);printf(“%s”, buf); }

6. 1- /* Detecting end-of-file. */ 2- #include <stdio.h> 3- #include <stdlib.h> 4- #define BUFSIZE 100 5- 6- main() 7- { 8- char buf[BUFSIZE]; 9- char filename[20]; 10- FILE *fp; 11- 12- puts("Enter name of text file to display: "); 13- gets(filename); /* Open the file for reading. */ 14- 15- if ( (fp = fopen(filename, "r")) == NULL) 16- { 17- fprintf(stderr, "Error opening file."); 18- exit(1); 19- } 20- 21- /* If end of file not reached, read a line and display it. */ 22- while ( !feof(fp) ) 23- { 24- fgets(buf, BUFSIZE, fp); 25- printf("%s",buf); } fclose(fp); 26- }

7. Sample file

8. Sample output

9. Another EOF example /* feof example: byte counter */ #include <stdio.h> int main () { FILE * pFile; long n = 0; pFile = fopen ("myfile.txt","rb"); if (pFile==NULL) perror ("Error opening file"); else { while (!feof(pFile)) { fgetc (pFile); n++; } fclose (pFile); printf ("Total number of bytes: %d\n", n-1); } return 0; }

10. File Function Program Random access with fseek()

11. Definition fseek() sets the file position indicator associated with file stream according to the values of offset and origin and supports random access I/O operations • Function prototype: • intfseek(FILE *stream, long int offset, int origin) • Values for origin must be one of the 3 following macros • SEEK_SET: seek from start of file • SEEK_CUR: seek from current position • SEEK_END: seek from end of file • Return value of 0 implies success, nonzero value indicates failure

12. Purpose The Random access with fseek program creates a binary file, writes on it, reopens it and looks for specific elements within the data as requested by user input.

13. Outline and Flowchart: • Create file • fp = fopen(“RANDOM.DAT”, “wb”) • Write to file • fwrite(array, sizeof(int), MAX, fp) • Read file • fp = fopen(“RANDOM.DAT”, “rb”) • Seek and print file element • fseek(fp, (offset*sizeof(int)), SEEK_SET) • fread(&data, sizeof(int), 1, fp)

14. 1- /* Random access with fseek(). */ 2- #include <stdio.h> 3- #include <stdlib.h> 4- #include <io.h> 5- 6- #define MAX 50 7- 8- main() 9- { 10- FILE *fp; 11- int data, count, array[MAX]; 12- long offset; 13- 14- /* Initialize the array. */ 15- for (count = 0; count < MAX; count++) 16- array[count] = count * 10; 17- 18- /* Open a binary file for writing. */ 19- if ( (fp = fopen("RANDOM.DAT", "wb")) == NULL) 20- { 21- fprintf(stderr, "\nError opening file."); 22- exit(1); 23- } 24-

15. 25- /* Write the array to the file, then close it. */ 26- if ( (fwrite(array, sizeof(int), MAX, fp)) != MAX) 27- { 28- fprintf(stderr, "\nError writing data to file."); 29- exit(1); 30- } 31- fclose(fp); 32- 33- /* Open the file for reading. */ 34- if ( (fp = fopen("RANDOM.DAT", "rb")) == NULL) 35- { 36- fprintf(stderr, "\nError opening file."); 37- exit(1); 38- }

16. 40- /* Ask user which element to read. Input the element entered. */ 41- while (1) 42- { 43- printf("\nEnter element to read, 0-%d, -1 to quit: ",MAX-1); 44- scanf("%ld", &offset); 45- if (offset < 0) break; else if (offset > MAX-1) continue; 46- 47- /* Move the position indicator to the specified element. */ 48- if ( (fseek(fp, (offset*sizeof(int)), SEEK_SET)) != NULL) 49- { 50- fprintf(stderr, "\nError using fseek()."); 51- exit(1); 52- } 53- 54- /* Read in a single integer. */ 55- fread(&data, sizeof(int), 1, fp); 56- printf("\nElement %ld has value %d.", offset, data); 57- } 58- 59- fclose(fp); 60- }

17. Output

18. Another Fseek Example /* fseek example */ #include <stdio.h> int main () { FILE * pFile; pFile = fopen ( "example.txt" , "w" ); fputs ( "This is an apple." , pFile ); fseek ( pFile , 9 , SEEK_SET ); fputs ( " sam" , pFile ); fclose ( pFile ); return 0; }

19. Questions or comments?

20. Thank you for your time!