![Example
#include <stdio.h>
int main()
{
FILE *f;
char buffer[11];
if (f = fopen("fred.txt",“r”))
{
fread(buffer, 1, 10, f);
buffer[10] = 0;
fclose(f);
printf("first 10 characters of the file:n%sn", buffer);
}
return 0;
}](https://image.slidesharecdn.com/lecture20-filehandling-190525182956/85/Lecture-20-File-Handling-20-320.jpg)
![Example
#include <stdio.h>
int main()
{
char a[10]={'1','2','3','4','5','6','7','8','9','a'};
FILE *fs;
fs=fopen("Project.txt","w");
fwrite(a,1,10,fs);
fclose(fs);
return 0;
}](https://image.slidesharecdn.com/lecture20-filehandling-190525182956/85/Lecture-20-File-Handling-22-320.jpg)
Lecture 20 - File Handling
- 1. File Handling Md. Imran Hossain Showrov ([email protected]) 20 1
- 2. Outline What is a File? Steps in Processing a File The Basic File Operations File Open Modes File Open Closing a File Reading and Writing Files
- 3. What is a File? A file is a collection of related data that a computers treats as a single unit. Computers store files to secondary storage so that the contents of files remain intact when a computer shuts down. When a computer reads a file, it copies the file from the storage device to memory; when it writes to a file, it transfers data from memory to the storage device. C uses a structure called FILE (defined in stdio.h) to store the attributes of a file.
- 4. Steps in Processing a File 1. Create the stream via a pointer variable using the FILE structure: FILE *p; 2. Open the file, associating the stream name with the file name. 3. Read or write the data. 4. Close the file.
- 5. The Basic File Operations fopen - open a file- specify how its opened (read/write) and type (binary/text) fclose - close an opened file fread - read from a file fwrite - write to a file fseek/fsetpos - move a file pointer to somewhere in a file. ftell/fgetpos - tell you where the file pointer is located.
- 7. File Open Modes: In Addition r+ - open for reading and writing, start at beginning w+ - open for reading and writing (overwrite file) a+ - open for reading and writing (append if file exists)
- 8. File Open The file open function (fopen) serves two purposes: It makes the connection between the physical file and the stream. It creates “a program file structure to store the information” C needs to process the file. Syntax: filepointer=fopen(“filename”,“mode”);
- 9. More On fopen The file mode tells C how the program will use the file. The filename indicates the system name and location for the file. We assign the return value of fopen to our pointer variable: spData = fopen(“MYFILE.TXT”,“w”); spData = fopen(“A:MYFILE.TXT”,“w”);
- 10. More On fopen
- 11. Closing a File When we finish with a mode, we need to close the file before ending the program or beginning another mode with that same file. To close a file, we use fclose and the pointer variable: fclose(spData);
- 12. fprintf() Syntax: fprintf (fp,"string",variables); Example: – int i = 12; – float x = 2.356; – char ch = 's'; – FILE *fp; – fp=fopen(“out.txt”,”w”); – fprintf (fp, "%d %f %c", i, x, ch);
- 13. fscanf() Syntax: fscanf (fp,"string",identifiers); Example: – FILE *fp; – Fp=fopen(“input.txt”,”r”); – int i; – fscanf (fp,“%d",i);
- 14. getc() Syntax: identifier = getc (file pointer); Example: FILE *fp; fp=fopen(“input.txt”,”r”); char ch; ch = getc (fp);
- 15. putc() Write a single character to the output file, pointed to by fp. Example: FILE *fp; char ch; putc (ch,fp);
- 16. End of File There are a number of ways to test for the end-of-file condition. Another way is to use the value returned by the fscanf function: FILE *fptr1; int istatus ; istatus = fscanf (fptr1, "%d", &var) ; if ( istatus == feof(fptr1) ) { printf ("End-of-file encountered.n”) ; }
- 17. Reading and Writing Files #include <stdio.h> int main ( ) { FILE *outfile, *infile ; int b = 5, f ; float a = 13.72, c = 6.68, e, g ; outfile = fopen ("testdata", "w") ; fprintf (outfile,“ %f %d %f ", a, b, c) ; fclose (outfile) ; infile = fopen ("testdata", "r") ; fscanf (infile,"%f %d %f", &e, &f, &g) ; printf (“ %f %d %f n ", a, b, c) ; printf (“ %f %d %f n ", e, f, g) ; }
- 18. Example #include <stdio.h> #include<conio.h> void main() { char ch; FILE *fp; fp=fopen("out.txt","r"); while(!feof(fp)) { ch=getc(fp); printf("n%c",ch); } getch(); }
- 19. fread () Declaration: size_t fread(void *ptr, size_t size, size_t n, FILE *stream); Remarks: fread reads a specified number of equal-sized data items from an input stream into a block. ptr = Points to a block into which data is read size = Length of each item read, in bytes n = Number of items read stream = file pointer
- 20. Example #include <stdio.h> int main() { FILE *f; char buffer[11]; if (f = fopen("fred.txt",“r”)) { fread(buffer, 1, 10, f); buffer[10] = 0; fclose(f); printf("first 10 characters of the file:n%sn", buffer); } return 0; }
- 21. fwrite() Declaration: size_t fwrite(const void *ptr, size_t size, size_t n, FILE*stream); Remarks: fwrite appends a specified number of equal-sized data items to an output file. ptr = Pointer to any object; the data written begins at ptr size = Length of each item of data n =Number of data items to be appended stream = file pointer
- 22. Example #include <stdio.h> int main() { char a[10]={'1','2','3','4','5','6','7','8','9','a'}; FILE *fs; fs=fopen("Project.txt","w"); fwrite(a,1,10,fs); fclose(fs); return 0; }