Thread: Segmentation faults!

here is the basic idea of my program, its a library takes a file of titles, BORROW, RETURN, SHELVE, lines each line indicating an operation. In my first implementation i used a 2d array to store my titles, and the number of titles was limited. Now i have to use malloc() to store the information. When i increase the size of allocated memory i start running into problems indirectly. For example, once i have done increased the size of the allocated memory i can print out the entire library without a problem. Then i can continuely access each element for searching purposes without a problem until a certain point. ie I would search the library maybe 3 times and on the third time when i try to access book 67 i get a segmentation fault. It seems to come from nowhere, a second ago i could access it and then suddenly i cant????? Has anyone had experience with a problem like this and might happen to know where the problems may lie? if you would like me to post my code i will, but im basically looking for someone that my have come across this problem before. Also, i programming in strictly ansi c if that matters. CHEERS

Alright, here is the doubling of the allocated memory:
if(bookline>=(n-2))
{
n=2*n;
temp1 =(char **)malloc(n*sizeof(char));
if(temp1 == NULL)
{
printf("ERROR\n");
return (1);
}
temp2 =(int *)malloc(n*sizeof(int));
if(temp2 == NULL)
{
printf("ERROR\n");
return (1);
}
for(i=0;i<n/2;i++)
{
temp1[i]=books[i];
temp2[i]=status[i];
}
free(books);
free(status); /*Questionable?*/
books = temp1;
status = temp2;
}
After that has happened, the final book has been added to the library and we now have a list of BORROW lines coming from the input, so we are continously entering a the BORROW if statement below.
else if(buffer[0] == 'B')
{

/*makes sure the last occurence of title is fully over written with nulls*/
for(nullify=0;nullify<80;nullify++)
{
title[nullify]='\0';
}

/*continues to assign a copy the buffer into books until two quotes have been met*/
while(indicator != 2)
{
/*the position is 7 spaces over to account for BORROW*/
title[pos] = buffer[7+pos];
if(buffer[7+pos] == '\"')
{
indicator++;
}
pos++;
}
/* THE PROBLEM ARISES IN THE INDEX_OF(TITLE) FUNCTION */
/*status is changed to unavailable*/
status[index_of(title)]=0;
}

and now for the index_of(title) function where the seg fault occurs while accessing "books[]"

int index_of(char *key)
{
int index =-1;
int t;
if(key == NULL)
{
return -1;
}

for(t=0;t<bookline;t++)
{

/*printf("book:%d\n",t);*/
/* THIS IS WHERE IT SEG FAULTS */
if(strcmp(key,books[t])) == 0)
{
return (t);
}
}
return (index);
}
It must be pointed out that these are the only options "touching" books and that in B if statement i have successfully printed(accessed) all the books until suddenly when i try and access a certain book i get a seg fault. I know this is not the best implementation, i am still new to C and the ins and outs. Either way cheers for your time Prelude.

I declared books and temp1 as a double pointer because I wanted each index to point to an array of characters aka a string. The problem lied in the fact that I was only allocating space for a char, not a title([code] char *title=(char *)malloc(80*sizeof(char)[\code]), by placing "title" in the sizeof parenthesises i fixed the seg fault. I'm not really sure why it was messing up as it did, but the problem is fixed. Visually, i did this:
[code]
/* Old: temp1 =(char **)malloc(n*sizeof(char)); */
temp1 = (char **)malloc(n*sizeof(title));
[\code]

Thanks a lot for the help/suggestions guys, also the links posted by prelude will help me ask my question the right way the next time I post. Cheers