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Listing Two
// bkcode
#include
#include
#include
#include
#define N_CAPITAL_LETTERS 26
#define LTRTOIDX(x) (x-'A')
int main(int argc, char *argv[])
{
char plain[_MAX_PATH], codfile[_MAX_PATH];
char cipher[_MAX_PATH], positions[_MAX_PATH];
char drive[_MAX_DRIVE];
char dir[_MAX_DIR];
char fname[_MAX_FNAME];
char ext[_MAX_EXT];
FILE *fp_plain, *fp_cod, *fp_cipher, *fp_pos;
long pos[N_CAPITAL_LETTERS];
int ch_plain, ch_cod;
// Argument processing
if (argc != 3) goto error1;
_splitpath(argv[1], drive, dir, fname, ext );
if (strlen(ext) == 0) strcpy(ext, "cod");
_makepath(codfile, drive, dir, fname, ext);
_makepath(positions, drive, dir, fname, "pos");
_splitpath(argv[2], drive, dir, fname, ext );
if (strlen(ext) == 0) strcpy(ext, "txt");
_makepath(plain, drive, dir, fname, ext);
_makepath(cipher, drive, dir, fname, "cry");
// File opening
if ((fp_plain = fopen(plain, "r")) == NULL) goto error3;
if ((fp_cod = fopen(codfile, "r")) == NULL) goto error3;
if ((fp_cipher = fopen(cipher, "w")) == NULL) goto error3;
fp_pos = fopen(positions, "rb+");
// Position array intialization
if (fp_pos == NULL) memset(pos, 0, sizeof(pos));
else {
fread(pos, sizeof(long), N_CAPITAL_LETTERS, fp_pos);
fclose(fp_pos);
}
// Main loop
do {
ch_plain = toupper(getc(fp_plain));
if (isalpha(ch_plain))
{
fseek(fp_cod, pos[LTRTOIDX(ch_plain)], SEEK_SET);
do {
ch_cod = getc(fp_cod);
} while (!(ch_cod == ch_plain || ch_cod == EOF));
if (ch_cod == ch_plain) {
pos[LTRTOIDX(ch_plain)] = ftell(fp_cod);
fprintf (fp_cipher, "%1ld ", pos[LTRTOIDX(ch_plain)]);
} else goto error2;
}
} while (ch_plain != EOF);
// Termination
fp_pos = fopen(positions, "wb");
fwrite (pos, sizeof(long), N_CAPITAL_LETTERS, fp_pos);
fclose(fp_plain); fclose(fp_cod); fclose(fp_cipher); fclose(fp_pos);
return 0;
// Error handling
error1: printf ("USAGE: bkcode codfile message\n"); return 1;
error2: printf ("Run out of letters %c!\n", ch_plain);
fclose(fp_plain); fclose(fp_cod);
fclose(fp_cipher); remove(cipher); return 1;
error3: printf ("Can not open files\n"); return 1;
}
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