Concept of File Handling in C Programming
To access any file, we need to declare a pointer to FILE structure and then associate it with particular file. Pointer is used to declare the file fainter.
FILE *fp;
2. Random File Processing:
a) fseek() :-The function fseek() is used to set the file position.
Its syntax is:
long ftell(FILE *fp);
Its syntax is:
rewind(FILE *fp);
There are following file operations
a) Creation of a new file
b) Opening an existing file
c) Reading from a file
d) Writing a file
e) Moving to a file in a specific location
f) Closing a file
File manipulation function
Character I/O
Declaration :
int fputc( int c, FILE *fptr);
This function writes a character to the specified file at the current file position and then increments the file pointer position.Declaration :
int fgetc(FILE *fptr);
It is used to read the single character form the file.
getc( ) and putc( )
The operations of getc( ) and putc( ) are exactly similar to that of fgetc( ) and fputc( ), the only difference is that the former two are defined as macros.
Integer I/O
putw( )
Declaration:
int putw(int value, FILE *fptr)
This function writes an integer value to the file pointed to by fptr.
getw( )
Declaration :
int getw(FILE *fptr);
This function returns the integer value from the file associated with fptr.
String I/O
fputs( )
Declaration:
int fputs(const char *str, FILE *fptr);
It means file put string. It writes the string for output.
fgets( )
Declaration:
char *fgets(char *str, int n, FILE *fptr);
This function is used to read characters from a file and these characters are stored in the string pointed by str.
Formatted I/O
fprintf( )
Declaration:
fprintf( FILE *fptr, const char *format[arguments]);
This function is same as the printf( ) function but it stores the data in data file.
fscanf( )
Declaration:
It works as a same as a scanf( ) function but it reads data from a the file instead the of standard input device, so it has one more parameter which is a pointer of FILE type and it points to the file from which data will be read.
Declaration:
size_t fwrite(const void *ptr,size_t size,size_t n,FILE *fptr);
It is used for writing an entire line.
fread( )
Declaration:
size_t fread(void *ptr, size_t size, size_t n, FILE *fptr);
It is used to read an entire given file.
Renaming and deleting file
Function remove( ) is used to delete the file whose syntax is as follows:
remove(filename);
Function rename( ) is used to rename old file name into new file name. Its syntax is as follows:
rename(old_file_name,new_file_name);
Opening, Reading, Writing and Appending data file
Opening a file
A file must be opened before any input/output operations performed on that file.
Syntax:
FILE *fopen(const char *filename, const char *mode);
fopen() function takes two strings as arguments, the first one is the name of the file to be opened and the second one is the mode that decides which operations are to be performed on the file.
FILE *fp1,fp2;
fpl = fopen(“myfile.txt”,“w”);
fp2 = fopen(“yourfile.dat”,“r”);
"w” (write)
If the file doesn’t exist then this mode creates a new file for writing, and if the file already exists then the previous data is erased and new data entered is written to the file.
“a” (append)
Open an existing text file for appending.
“r” (read)
Open an existing file for read only.
“w+” (write + read)
Open a new file for reading and writing. In case of existing file, it will destroy, and new file will be created.
“r+” (read + write)
It Open an existing file for both reading and writing purpose.
“a+” (append + read)
It Opens an existing data file for reading and appending.
We can use fscanf() and fgets() functions to read the file.
Syntax:
fscanf(<file pointer>, <”format specifier”>,< variable>);
fscanf(filePointer, "%s %s %d", str1, str2,, &yr);
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Example: 1 File reading using scanf. #include<stdio.h> #include<conio.h> void main() { clrscr(); FILE *fptr; char str[100]; fptr=fopen("AVN.TXT","r"); printf("%d\n",fptr); do { fscanf(fptr,"%s",str); printf("%s ",str); } while(!feof(fptr)); fclose(fptr); getch(); } |
Example: 2 File Reading using fgetc #include <stdio.h> int main() { char ch; FILE *fp; fp = fopen("abc.txt", "w+"); while( (ch=fgetc(fp)) != EOF ) { printf("%c", ch); } fclose(fp); return 9; } |
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Example 3: File Reading using fgets. #include <stdio.h> int main() { char str[80]; FILE *fp; fp = fopen("abc.txt", "w+"); while( (fgets(str, 79, fp)) != NULL ) { printf("%s", str); } fclose(fp); return 0; } |
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Writing a file
In writing file operation fprintf(), and fputs() functions are used to store the data in data file.
FILE *filePointer ;
filePointer = fopen(“fileName.txt”, “w”);
fprintf(<file pointer>, <”text to be written to file”>,….);
Example: 1
#include <stdio.h>
int main()
{
FILE *fp;
file = fopen("file.txt","w"); // Create a file and add text
fprintf(fp,"%s","This is just an example");
fclose(fp);
return 0;
}
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Example 2: File Writing using fputc #include <stdio.h> int main() { char str[]= "Welcome to file handling"; int i=0; FILE *fp; fp = fopen("abc.txt", "a"); while( str[i] != '\0' ) { fputc(str[i], fp); i++; } fclose(fp); return 0; } |
Example 3: File Writing using fputs String by String #include <stdio.h> int main() { char str[]= "RAM and Shyam "; FILE *fp; fp = fopen("abc.txt", "a"); fputs(str, fp); fclose(fp); return 0; } |
File Append mode
Append mode add more data at the end f the exiting file. It cannot overwrite an existing file.
Syntax:
FILE *fopen(const char *filename, const char *mode)
OR
FILE *fp = fopen(<path>, "a");
FILE *fp = fopen(<path>, "a+");
Closing a File
To close the file we use fclose() function.
Syntax:
fclose(FILE *fptr);
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