Segmentation fault (core dumped)...BMH Algorithm - c

Question

I am trying to implement a Boyer Moore Horsepoole algorithm. This code was written in Turbo C++, Windows. It worked. I have to port this in ubuntu.
typedef struct skip_table
{
char index;
int value;
}skip_table;
void create_table(char*,int);
int discrete_char(char*,int);
int bm(char*, char*);
int lookup(char);
int check_EOF(char*,int);
skip_table *t1;
int tab_len;
FILE *fptr;
int main()
{
time_t first, second;
double time_spent;
long int cnt=0;
char *key_string,*buf,c; // String to be matched and text
int i,key_len,text_len,def_shift_len,flag_match=0;
gets(key_string);
key_len=strlen(key_string);
fptr=fopen("test_file.txt","r");
first = clock();
fseek(fptr,SEEK_SET,0);
create_table(key_string,key_len);
while(flag_match!=1)
{
fseek(fptr,100*cnt,0);
fread(buf,100-key_len-1, 1, fptr);
flag_match = bm(buf, key_string);
cnt++;
printf("\n%d",cnt);
}
second =clock();
time_spent=(double)(second-first)/CLOCKS_PER_SEC;
if(flag_match==1)
printf("\n\nMatch Found in %lf seconds",time_spent);
else
printf("\n\nMatch NOT Found in %lf seconds",time_spent);
fclose(fptr);
return 0;
}
int discrete_char(char* key_string,char* temp,int key_len)
{
int i,j,count=1,flag=0;
for(i=1;i<key_len;i++)
{
for(j=0; j<count; j++)
{
flag=0;
if(temp[j] == key_string[i])
{
flag=1;
break;
}
}
if(flag!=1)
{
temp[count++]=key_string[i];
flag=0;
}
}
temp[count]='\0';
return count;
}
void create_table(char* key_string,int key_len)
{
int i,j,k,max_index;
char *temp;
temp[0] = key_string[0];
tab_len=discrete_char(key_string,temp,key_len);
t1=(skip_table*)malloc((tab_len-1)*sizeof(skip_table));
for(i=0;i<tab_len;i++)
{
for(j=0;j<key_len;j++)
{
if(temp[i]==key_string[j])
max_index=j;
}
t1[i].index=temp[i];
t1[i].value=key_len-max_index-1;
printf("\n\n %c %d",t1[i].index,t1[i].value);
}
}
int bm(char* text, char* key_string)
{
int i_t, i_k, j,k, text_len, key_len, shift, count=0, flag_match=0;
int loop_count;
text_len = strlen(text);
key_len = strlen(key_string);
i_t=key_len;
i_k=key_len;
loop_count=0;
while(i_t<=text_len)
{
if(count != key_len)
{
if(text[i_t-1]==key_string[i_k-1])
{
count++;
i_t--; i_k--;
loop_count++;
}
else
{
if(loop_count>key_len)
{
i_t=i_t+lookup(text[i_t-1])+1;
i_k=key_len;
loop_count=0;
continue;
}
shift = lookup(text[i_t-1]);
if(shift<=0)
shift=key_len;
i_t = i_t+shift;
i_k = key_len;
count=0;
}
}
else
{
flag_match = 1;
break;
}
}
return flag_match;
}
"int lookup(char index)" returns the respective value field of the index if present in "temp" else returns -1.
There's my whole code.

Answer 1

Not that I see exactly what went wrong but here are some defensive programming tips:
int main()
{
// initialize all variables before use
time_t first = 0, second = 0;
double time_spent = 0.0;
long int cnt=0;
char *key_string = NULL;
char *buf = NULL;
char c = '\0';
char temp[50] = {0};
int i = 0,key_len=0,text_len=0,def_shift_len=0,flag_match=0;
// use fgets instead of gets, fgets allows you specify max length
fgets(temp,sizeof(temp),stdin);
key_len=strlen(temp);
key_string = (char*) malloc(key_len+1);
// use strncpy or strcpy_s to specify max size
strncpy(key_string, temp, sizeof(key_string));
fptr = fopen("test_file.txt","r");
first = clock();
// here arguments have wrong order, fseek takes origin as last arg:
fseek(fptr,0,SEEK_SET);
// could be something in create_table, but you have not supplied it
create_table(key_string,key_len);
When you have so many variables in a function you may consider moving out parts of the function to other functions

Answer 2

Try using --track-origins=yes on your valgrind options as well, as the output suggests, this can help track down where uninitialised varables have come from.
As others have suggested, the issue valgrind is reporting is inside create_table, so please post the code for that as well.