Code:
#include stdio.h
#include errno.h
long count_characters(FILE *);
void main(int argc, char * argv[])
{
int i;
long cnt;
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)
{
ch = fgetc(fp1);
fputc(ch, fp2);
fseek(fp1, -2L, 1); // shifts the pointer to the previous character
cnt--;
}
printf("\n**File copied successfully in reverse order**\n");
}
else
{
perror("Error occured\n");
}
fclose(fp1);
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;
}
Output:
**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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