file handling in c programming with file functions

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.

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.

The basic file operations are
• 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.

File Open Modes
from Table 7-1 in Forouzan & Gilberg, p. 400

More on File Open Modes
from Figure 7-4 in Forouzan & Gilberg, p. 401

Additionally,
• 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)

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”);

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”);

More On fopen
from Figure 7-3 in Forouzan & Gilberg, p. 399

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);

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);

fscanf()
Syntax:
fscanf (fp,"string",identifiers);
Example:
FILE *fp;
Fp=fopen(“input.txt”,”r”);
int i;
fscanf (fp,“%d",i);

getc()
Syntax:
identifier = getc (file pointer);
Example:
FILE *fp;
fp=fopen(“input.txt”,”r”);
char ch;
ch = getc (fp);

putc()
write a single character to the output file,
pointed to by fp.
Example:
FILE *fp;
char ch;
putc (ch,fp);

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”) ;
}

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) ;
}

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();
}

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

Example
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;
}

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

Example
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;
}

fseek()
This function sets the file position indicator for the stream pointed to by stream or you can
say it seeks a specified place within a file and modify it.
SEEK_SET Seeks from beginning of file
SEEK_CUR Seeks from current position
SEEK_END Seeks from end of file
Example:
#include <stdio.h>
int main()
{
FILE * f;
f = fopen("myfile.txt", "w");
fputs("Hello World", f);
fseek(f, 6, SEEK_SET); SEEK_CUR, SEEK_END
fputs(" India", f);
fclose(f);
return 0;
}

ftell()
offset = ftell( file pointer );
"ftell" returns the current position for input or output on the file
#include <stdio.h>
int main(void)
{
FILE *stream;
stream = fopen("MYFILE.TXT", "w");
fprintf(stream, "This is a test");
printf("The file pointer is at byte %ldn", ftell(stream));
fclose(stream);
return 0;
}

file handling in c programming with file functions

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