69 lines
2.3 KiB
C
69 lines
2.3 KiB
C
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/*
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* C Program to Reverse the Contents of a File and Print it
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*/
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#include <stdio.h>
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#include <errno.h>
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long count_characters(FILE *);
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void main(int argc, char * argv[])
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{
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int i;
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long cnt;
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char ch, ch1;
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FILE *fp1, *fp2;
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if (fp1 = fopen(argv[1], "r"))
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{
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printf("The FILE has been opened...\n");
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fp2 = fopen(argv[2], "w");
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cnt = count_characters(fp1); // to count the total number of characters inside the source file
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fseek(fp1, -1L, 2); // makes the pointer fp1 to point at the last character of the file
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printf("Number of characters to be copied %d\n", ftell(fp1));
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while (cnt)
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{
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ch = fgetc(fp1);
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fputc(ch, fp2);
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fseek(fp1, -2L, 1); // shifts the pointer to the previous character
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cnt--;
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}
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printf("\n**File copied successfully in reverse order**\n");
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}
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else
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{
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perror("Error occured\n");
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}
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fclose(fp1);
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fclose(fp2);
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}
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// count the total number of characters in the file that *f points to
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long count_characters(FILE *f)
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{
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fseek(f, -1L, 2);
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long last_pos = ftell(f); // returns the position of the last element of the file
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last_pos++;
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return last_pos;
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}
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/*
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$ gcc file12.c
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$ cat test2
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The function STRERROR returns a pointer to an ERROR MSG STRING whose contents are implementation defined.
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THE STRING is not MODIFIABLE and maybe overwritten by a SUBSEQUENT Call to the STRERROR function.
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$ a.out test2 test_new
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The FILE has been opened..
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Number of characters to be copied 203
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**File copied successfully in reverse order**
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$ cat test_new
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.noitcnuf RORRERTS eht ot llaC TNEUQESBUS a yb nettirwrevo ebyam dna ELBAIFIDOM ton si GNIRTS EHT
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.denifed noitatnemelpmi era stnetnoc esohw GNIRTS GSM RORRE na ot retniop a snruter RORRERTS noitcnuf ehT
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$ ./a.out test_new test_new_2
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The FILE has been opened..
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Number of characters to be copied 203
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**File copied successfully in reverse order**
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$ cat test_new_2
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The function STRERROR returns a pointer to an ERROR MSG STRING whose contents are implementation defined.
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THE STRING is not MODIFIABLE and maybe overwritten by a SUBSEQUENT Call to the STRERROR function.
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$ cmp test test_new_2
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