Having problems with fprintf - c

Question

I am trying to write a code that simulates an Anti-Virus scan, it scans 5 specific files and then creates a file named AntiVirusLog.txt. In this file it writes the results, for example PSY.avi INFECTED. An infected file is a file that contains the string in the file youtubesign.
My problem is when I try to print in the results to the file AntiVirusLog.txt it does not print anything and leaves the file blank.
My code:
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<dirent.h>
#define BUZZ_SIZE 1024
int fast_scan(char *fname, char *str, FILE *fs);
int slow_scan(char *fname, char *str, FILE *fs);
int main(int argc, char *argv[])
{
char name[100];
char choice[5];
char buff[BUZZ_SIZE];
FILE *f7, *f2;
struct dirent *de;
DIR *dr = opendir(argv[1]);
if (dr == NULL) // opendir returns NULL if couldn't open directory
{
printf("Could not open current directory");
return 0;
}
f2 = fopen(argv[2], "rb");
f7 = fopen("AntiVirusLog.txt", "wt");
printf("Welcome to Amnon's Anti-Virus program\n which scan would you like to choose?:\n");
printf("Fast: check only the first and the last 20% of the file\n Slow: Checks the entire file\n");
printf("Enter fast for a fast scan and slow for a slow scan\n");
scanf("%s", choice);
if ((strcmp(choice, "slow"))==0)
{
while ((de = readdir(dr)) != NULL)
{
strcpy(name, argv[1]);
strcat(name, de->d_name);
if((fgets(buff, BUZZ_SIZE, f2)) != NULL)
{
slow_scan(name, buff, f7);
}
}
}
if ((strcmp(choice, "fast")) == 0)
{
while ((de = readdir(dr)) != NULL)
{
strcpy(name, argv[1]);
strcat(name, de->d_name);
if ((fgets(buff, BUZZ_SIZE, f2)) != NULL)
{
fast_scan(name, buff, f7);
}
}
}
printf("The scan was made successfuly, check the file AntiVirusLog.txt to see the results\n");
closedir(dr);
fclose(f2);
fclose(f7);
system("PAUSE");
return (0);
}
int slow_scan(char *fname, char *str, FILE *fs)
{
int findres = 0;
FILE *fp;
char temp[BUZZ_SIZE];
if ((fopen_s(&fp, fname, "rb")) != NULL)
{
return(-1);
}
while ((fgets(temp, BUZZ_SIZE, fp)) != NULL)
{
if ((strstr(temp, str)) != NULL)
{
fprintf(fs, "%s INFECTED\n", fname);
findres++;
}
}
if (findres==0)
{
fprintf(fs, "%s NOT INFECTED\n", fname);
}
fclose(fp);
return(0);
}
int fast_scan(char *fname, char *str, FILE *fs)
{
int findres=0;
int i, j, len, partlen;
FILE *fp;
if ((fopen_s(&fp, fname, "rb")) != NULL)
{
return(-1);
}
fseek(fp, 0, SEEK_END);
len = ftell(fp);
partlen = (len * 20) / 100;
char *temp=malloc(partlen);
while ((fgets(temp, BUZZ_SIZE, fp)) != NULL)
{
for (i = 0; i < partlen; i++)
{
if (temp[i]=str[i])
{
findres++;
}
if (temp[i] != str[i])
{
i = partlen + 1;
}
if (findres == partlen)
{
fprintf(fs, "%s INFECTED\n", fname);
i = partlen + 1;
}
}
for (j = len - partlen; j < len; j++)
{
if (temp[j] = str[j])
{
findres++;
}
if (temp[j] != str[j])
{
j = partlen + 1;
}
if (findres == partlen)
{
fprintf(fs, "%s INFECTED\n", fname);
j = partlen + 1;
}
}
}
if (findres!= partlen)
{
fprintf(fs, "%s NOT INFECTED\n", fname);
}
fclose(fp);
return(0);
}

Answer 1

There are primarily two major issues with your code
Point 1: In your code, for the series of calls like
search_sign(argv[1], buff, f7);
you're using buff uninitialized. The buff is then passed as the second parameter of search_sign(), (to be accepted as str) which is again used as the search string in strstr().
As buff is an automatic local variable, the initial content (value) is garbage (indeterminate) and hence , when used as the search key in strstr(), will invoke undefined behaviour.
Point 2: That said, as my previous comment, you should always be checking the success of fopen() call(s) before using the returned file pointer any further.

Answer 2

I have used some of the advices listen and found some fixes of my own and now it works perfectly! the updated code looks like this:
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define BUZZ_SIZE 1024
int search_sign(char *fname, char *str, FILE *fs);
int main(int argc, char *argv[])
{
char buff[BUZZ_SIZE];
FILE *f,*f7;
f7 = fopen("AntiVirusLog.txt", "wt");
f = fopen(argv[1], "rb");
if ((fgets(buff, BUZZ_SIZE, f)) != NULL)
{
search_sign(argv[2], buff, f7);
search_sign(argv[3], buff, f7);
search_sign(argv[4], buff, f7);
search_sign(argv[5], buff, f7);
search_sign(argv[6], buff, f7);
}
printf("The scan was made successfuly, check the file AntiVirusLog.txt to see the results\n");
fclose(f);
fclose(f7);
system("PAUSE");
return (0);
}
int search_sign(char *fname, char *str, FILE *fs)
{
int findres = 0;
FILE *fp;
char temp[BUZZ_SIZE];
if ((fopen_s(&fp, fname, "rb")) != NULL)
{
return(-1);
}
while ((fgets(temp, BUZZ_SIZE, fp)) != NULL)
{
if ((strstr(temp, str)) != NULL)
{
fprintf(fs, "%s INFECTED\n", fname);
findres++;
}
}
if (findres==0)
{
fprintf(fs, "%s NOT INFECTED\n", fname);
}
fclose(fp);
return(0);
}