LECTURE 22-23: Text and Binary File Processing (Chapter 12)

File Pointer Variables

// To declare a file pointers for input and output text files

FILE *infilep;

FILE *outfilep

// To initialize infilep to point to file b:date.txt that is read-only

infilep = fopen(“b:data.txt”, “r”);

// Check if file was opened successfully

if (infilep == NULL)

printf(“Cannot open the file \n”)

// To initialize outfilep

outfilep = fopen(“b:results.txt”,”w”);

Text File Processing

The opened files can be read from and manipulated using the following functions that can take file pointer arguments:

fscanf, fprintf, getc, putc

These functions are analogous to

scanf, printf, getchar, putchar

Read TABLE 12.4 to understand the differences between these two groups of functions!

// To close both files

fclose(infilep);

fclose(outfilep);

Useful example (FIGURE 12.1) : Program to Make a Backup Copy of a Text File

/*

* Makes a backup file. Repeatedly prompts for the name of a file to

* back up until a name is provided that corresponds to an available

* file. Then it prompts for the name of the backup file and creates

* the file copy.

*/

#include <stdio.h>

#define STRSIZ 80

int main(void)

{

char in_name[STRSIZ], /* strings giving names */

out_name[STRSIZ]; /* of input and backup files */

FILE *inp, /* file pointers for input and */

*outp; /* backup files */

char ch; /* one character of input file */

/* Get the name of the file to back up and open the file for input */

printf("Enter name of file you want to back up> ");

for (scanf("%s", in_name);

(inp = fopen(in_name, "r")) == NULL;

scanf("%s", in_name)) {

printf("Cannot open %s for input\n", in_name);

printf("Re-enter file name> ");

}

/* Get name to use for backup file and open file for output */

printf("Enter name for backup copy> ");

for (scanf("%s", out_name);

(outp = fopen(out_name, "w")) == NULL;

scanf("%s", out_name)) {

printf("Cannot open %s for output\n", out_name);

printf("Re-enter file name> ");

}

/* Make backup copy one character at a time */

for (ch = getc(inp); ch != EOF; ch = getc(inp))

putc(ch, outp);

/* Close files and notify user of backup completion */

fclose(inp);

fclose(outp);

printf("Copied %s to %s.\n", in_name, out_name);

return(0);

}

Binary File Processing

Text files are useful for storing and processing text files. However, many data files are of different nature – for example, image, video, audio files. In this case, it is more efficient to use binary files.

Functions fread and fwrite are used to read and write to binary files, and they are analogous to fprintf and fscanf that are used for text files.

Example (FIGURE 12.3): Creating a Binary File of Integers

FILE *binaryp;

int i;

binaryp = fopen("nums.bin", "wb"); /* “wb” means that file is binary write-only */

for (i = 2; i <= 500; i += 2)

fwrite(&i, sizeof (int), 1, binaryp);

fclose(binaryp);

Let us consider arguments of fwrite function:

- &i is address of a number to be stored

- sizeof(int) informs computer about the number of bytes needed to store an integer

- 1 means that only one integer is to be written

- binaryp is a pointer to file where information is to be written

If we wanted to store to binary file an array of integers score declared as

int score[10];

we would write

fwrite(score, sizeof(int), 10, binaryp);

For more detailed explanation about the differences between text and binary file processing, check TABLE 12.5!!