Getting a C++ segmentation fault - c++

Question

I'm in a linux server and when I try to execute the program it's returning a segmentation fault. when i use gdb to try and find out why, it returns..
Starting program: /home/cups/k
Program received signal SIGSEGV, Segmentation fault.
0x0000000000401128 in search(int) ()
Missing separate debuginfos, use: debuginfo-install glibc-2.12-1.192.el6.x86_64 libgcc-4.4.7-17.el6.x86_64 libstdc++-4.4.7-17.el6.x86_64
I couldn't quite interpret this. In my program i have a function called "search()" but i don't see anything that would cause a seg fault. here's the function def:
int search (int bit_type) { // SEARCH FOR A CONSEC NUMBER (of type BIT_TYPE) TO SEE IF ALREADY ENCOUNTERED
for (int i = 1; i <= MAX[bit_type]; i++) { //GO THRU ALL ENCOUNTERED CONSEC NUMBERS SO FAR (for type BIT_TYPE)
if (consec == r[bit_type][i]) // IF: FOUND
return i; // -----> RETURN INDEX OF RECORDED CONSEC_NUM
}
// IF: NOT FOUND
r[bit_type][++MAX[bit_type]] = consec; // -----> INCREMENT MAX[bit_type] & RECORD NEW CONSEC_NUM -------> ARRAY[MAX]
n[bit_type][MAX[bit_type]] = 1;
return (MAX[bit_prev]); // -----> RETURN THE NEWLY FILLED INDEX
}
global functions:
int MAX[2];
int r[2][200];
int n[2][200];
The comments are pretty useless to you guys since you don't have the rest of the program.. but you can just ignore them.
But do you guys see anything I missed?

Answer 1

From the link to your code here, here is just one error:
int *tmp = new int[MAX[0]];
for (int y = 0; y <= MAX[0]; y++) {
tmp[y] = 1;
}
You are going out-of-bounds on the last iteration. You allocated an array with MAX[0] items, and on the last iteration you're accessing tmp[MAX[0]].
That loop should be:
int *tmp = new int[MAX[0]];
for (int y = 0; y < MAX[0]; y++) {
tmp[y] = 1;
}
or better yet:
#include <algorithm>
//...
std::fill(tmp, tmp + MAX[0], 1); // no loop needed
or skip the dynamic allocation using new[] and use std::vector:
#include <vector>
//...
std::vector<int> tmp(MAX[0], 1);
In general, you have multiple loops that do this:
for (int i = 1; i <= number_of_items_in_array; ++i )
and then you access your arrays with array[i]. It is the <= in that for loop condition that is suspicious since it will try to access the array with an out-of-bounds index on the last iteration.
Another example is this:
long sum(int arr_r[], int arr_n[], int limit)
{
long tot = 0;
for (int i = 1; i <= limit; i++)
{
tot += (arr_r[i])*(arr_n[i]);
}
return tot;
}
Here, limit is the number of elements in the array, and you access arr_r[i] on the last iteration, causing undefined behavior.
Arrays are indexed starting from 0 and up to n - 1, where n is the total number of elements. Trying to fake 1-based arrays as you're attempting to do almost always results in these types of errors somewhere inside of the code base.