C Program to Print the Contents of File in Reverse Order

This C Program reverses the contents of a file and print it.

Here is source code of the C Program to reverse the contents of a file and print it. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

```
/* 
```

 * C Program to Reverse the Contents of a File and Print it

```
 */
```
```
#include <stdio.h>
```
```
#include <errno.h>
```
```
 
```
```
long count_characters(FILE *);
```
```
 
```
```
void main(int argc, char * argv[])
```
```
{
```
```
    int i;
```
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    long cnt;
```
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    char ch, ch1;
```
```
    FILE *fp1, *fp2;
```
```
 
```
```
    if (fp1 = fopen(argv[1], "r"))    
```
```
    {
```

        printf("The FILE has been opened...\n");

```
        fp2 = fopen(argv[2], "w");
```

        cnt = count_characters(fp1); // to count the total number of characters inside the source file

        fseek(fp1, -1L, 2);     // makes the pointer fp1 to point at the last character of the file

        printf("Number of characters to be copied %d\n", ftell(fp1));

```
 
```
```
        while (cnt)
```
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        {
```
```
            ch = fgetc(fp1);
```
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            fputc(ch, fp2);
```

            fseek(fp1, -2L, 1);     // shifts the pointer to the previous character

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            cnt--;
```
```
        }
```

        printf("\n**File copied successfully in reverse order**\n");

```
    }
```
```
    else
```
```
    {
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```
        perror("Error occured\n");
```
```
    }
```
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    fclose(fp1);
```
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    fclose(fp2);
```
```
}
```

// count the total number of characters in the file that *f points to

```
long count_characters(FILE *f) 
```
```
{
```
```
    fseek(f, -1L, 2);
```

    long last_pos = ftell(f); // returns the position of the last element of the file

```
    last_pos++;
```
```
    return last_pos;
```
```
}
```

$ gcc file12.c
$ cat test2
The function STRERROR returns a pointer to an ERROR MSG STRING whose contents are implementation defined.
THE STRING is not MODIFIABLE and maybe overwritten by a SUBSEQUENT Call to the STRERROR function.
$ a.out test2 test_new
The FILE has been opened..
Number of characters to be copied 203
 
**File copied successfully in reverse order**
$ cat test_new
 
.noitcnuf RORRERTS eht ot llaC TNEUQESBUS a yb nettirwrevo ebyam dna ELBAIFIDOM ton si GNIRTS EHT
.denifed noitatnemelpmi era stnetnoc esohw GNIRTS GSM RORRE na ot retniop a snruter RORRERTS noitcnuf ehT
$ ./a.out test_new test_new_2
The FILE has been opened..
Number of characters to be copied 203
 
**File copied successfully in reverse order**
$ cat test_new_2
The function STRERROR returns a pointer to an ERROR MSG STRING whose contents are implementation defined.
THE STRING is not MODIFIABLE and maybe overwritten by a SUBSEQUENT Call to the STRERROR function.
$ cmp test test_new_2

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