1. Lecture 27: FILE HANDLING in C Language FILE HANDLING in C Language-2 Lecture 27

2. Lecture 27: FILE HANDLING in C Language FILE pointer in C The statement: FILE *fptr1, *fptr2 ; fptr1fptr2 FILE declares that fptr1 and fptr2 are pointer type variables of type FILE. They can contain the address of a file descriptors.

3. Lecture 27: FILE HANDLING in C Language Opening FILE The statement: FILE *fptr1; fptr1 = fopen( d:\\mydata.txt", "r"); d:\\mydata.txt would open the file d:\\mydata.txt for input (reading). The statement: FILE *fptr2; fptr2 = fopen(d:\\results.txt", "w"); d:\\results.txt would open the file d:\\results.txt for output (writing).

4. Lecture 27: FILE HANDLING in C Language Opening Text Files The statement: FILE *fptr2; fptr2 = fopen (d:\\results.txt",r+"); d:\\results.txt would open the file d:\\results.txt for both reading and writing. Once the FILE is open, it stay open until you close it or end of the program reaches (which will close all files.)

5. Lecture 27: FILE HANDLING in C Language Testing for Successful Open fopenIf the FILE was not able to be opened, then the value returned by the fopen routine is NULL. d:\\mydata.txtFor example, let's assume that the file d:\\mydata.txt does not exist. Then: FILE *fptr1; fptr1 = fopen ( d:\\mydata.txt", W") ; if (fptr1 == NULL) cout<< "File 'mydata' cant be open; else cout << File opens successfully;

6. Lecture 27: FILE HANDLING in C Language Writing in FILE We can write any contents (data) in the FILE using the following FILING function: fprintf (paramter1, paramter2, paramter3); FILE pointerSignature of the variable Actual name of the variable

7. Lecture 27: FILE HANDLING in C Language Writing in FILE (Example 1) fprintf The fprintf function will write value from the number1 (memory location) to hard disk location (d:\\mydata.txt). void main (void) { FILE *fptr; fptr = fopen( d:\\mydata.txt, w ); // write mod int number1 = 93; fprintf (fptr,%d, number1); }

8. Lecture 27: FILE HANDLING in C Language Writing in FILE (Example 2) fprintf The fprintf function will write value from the number1 & floatData (memory location) to hard disk location (d:\\myfile.dat). void main (void) { FILE *fptr; fptr = fopen( d:\\myfile.dat, w ); // write mod long number1 = 93; float floatData = 34.63; fprintf (fptr,%d%f, number1,floatData); }

9. Lecture 27: FILE HANDLING in C Language Writing in FILE (Example 3) fprintf The fprintf function will write value from the number1, floatData and myCharacter (memory location) to hard disk location (d:\\mydata.txt). void main (void) { FILE *fptr; fptr = fopen(d:\\myfile.dat,w); // write mod long number1 = 93; float floatData = 34.63; char myCharacter = D; fprintf (fptr,%d%f%c, number1,floatData,myCharacter); }

10. Lecture 27: FILE HANDLING in C Language Writing in FILE (Example 4) fprintf The fprintf function will write value from the string 1 (memory location) to hard disk location (d:\\mydata.txt). void main (void) { FILE *fptr; fptr = fopen( d:\\myfile.dat, w ); // write mod char string1 [40]; strcpy (string1, My text information is Pakistan); fprintf (fptr,%s, string1); }

11. Lecture 27: FILE HANDLING in C Language Writing in FILE (problem with w MOD) What would be the final data in the FILE name myfile.data when the above code executes 3 times. The final data would be only (353) not (353353353). The reason is that, with w MOD, on every run the previous data is REMOVED, and the new data is written from beginning of FILE. void main (void) { FILE *fptr; fptr = fopen( d:\\myfile.dat, w ); // write mod int data = 353; fprintf (fptr,%d, data); }

12. Lecture 27: FILE HANDLING in C Language Solution Open in Append MOD a+ or w+ In append MOD, the previous data in the FILE is not removed on every new execution. The data in the FILE name d:\\myfile.data on the 3 runs would be now (353353353). void main (void) { FILE *fptr; fptr = fopen(d:\\myfile.dat,a+); // write mod int data = 353; fprintf (fptr,%d, data); }

13. Lecture 27: FILE HANDLING in C Language OUTLINE How we can read data/information from the FILES. How we can close the FILES.

14. Lecture 27: FILE HANDLING in C Language Reading from FILE We can write any contents (data) in the FILE using the following FILING function: returnParameter fscanf (paramter1, paramter2, paramter3); FILE pointer Signature of the variable Actual name of the variable End of file indicator

15. Lecture 27: FILE HANDLING in C Language Reading from FILE (Example 1) fscanf The fscanf function will read value from the hard disk location (d:\\mydata.txt) to number1 (memory location). void main (void) { FILE *fptr; fptr = fopen( d:\\mydata.txt, r+ ); // random mod int number1 = 93, number2 = 0; fprintf (fptr,%d, number1); fscanf (fptr,%d, &number2); }

16. Lecture 27: FILE HANDLING in C Language Reading from FILE (Example 2) void main (void) { FILE *fptr; fptr = fopen( d:\\myfile.dat, r+ ); // random mod long number1 = 93, read1 = 0; float floatData = 34.63, read2 = 0; fprintf (fptr,%d%f, number1,floatData); fscanf (fptr,%d%f,&read1,&read2); }

17. Lecture 27: FILE HANDLING in C Language Reading from FILE (Example 3) void main (void) { FILE *fptr; fptr = fopen(d:\\myfile.dat,r+); // random mod long number1 = 93, read1 = 0; float floatData = 34.63, read2 = 0; char myCharacter = D, read3 = ; fprintf (fptr,%d%f%c, number1,floatData,myCharacter); fscanf (fptr,%d%f%c,&read1, &read2, &read3); cout << Value are << read1 << read2 << read3; }

18. Lecture 27: FILE HANDLING in C Language Reading from FILE (Example 4) void main (void) { FILE *fptr; fptr = fopen( d:\\myfile.dat, r+ ); // random mod char string1 [40], string2 [40]; strcpy (string1, My text information is Pakistan); fprintf (fptr,%s, string1); fscanf (fptr,%s,string2); cout << string2; }

19. Lecture 27: FILE HANDLING in C Language Reading byte by byte Information from FILE (Example 5) void main (void) { FILE *fptr; fptr = fopen( d:\\myfile.dat, w ); // write mod char string1 [40]; strcpy (string1, My text information is Pakistan); fprintf (fptr,%s, string1); } void main (void) { FILE *fptr; fptr = fopen( d:\\myfile.dat, r ); // read mod char character; while (1) { fscanf (fptr,%c,&character); cout << character; } write.cpp read.cpp The problem with this code is that it can read out of the file data from your disk. Control it using End of file marker.

20. Lecture 27: FILE HANDLING in C Language End of file The end-of-file indicator informs the program when there are no more data (no more bytes) to be processed. fscanfThere are a number of ways to test for the end- of-file condition. One way is to use the value returned by the fscanf function: int istatus; istatus = fscanf (fptr1, "%d", &var) ; if ( istatus == EOF ) { cout << End-of-file encountered.; }

21. Lecture 27: FILE HANDLING in C Language Reading byte by byte Information from FILE (Example 6) void main (void) { FILE *fptr; fptr = fopen( d:\\myfile.dat, r ); // read mod char character; while (1) { int status = 0; status = fscanf (fptr,%c,&character); if ( status == EOF ) break; cout << character; } read.cpp

22. Lecture 27: FILE HANDLING in C Language Closing FILES The statements: fclose ( fptr1 ) ; fclose ( fptr2 ) ; will close the files and release the file descriptor space from memory.