Function Bad pointer runtime error? - c++

Question

I am trying to implement function that searches for match between two C-style strings, as a part of an exercise from "Programming: Principles and Practice using C++".
However, I am getting a runtime unhandled exception:
Access violation reading location 0x008ff000.
that breaks at a bad pointer value (indicated in the code).
#include <iostream>
char* find (char* s, char* x) {
// variable that stores the first char of matching substring of s
char* match = nullptr;
// control variable indicating full match between x and substring of s
bool full_match = false;
if (s == nullptr || x == nullptr) return match;
size_t len_s = my_strlen(s);
size_t len_x = my_strlen(x);
// x must be shorter than s
if (len_s < len_x) return match;
// pointers to beginning and end of s and x, used for traversal loops
char *s_begin = s;
char *s_end = s + len_s;
char *x_begin = x;
char *x_end = x + len_x;
// traverse s
for (char* i = s_begin; s_begin != s_end; ++i) {
// test for match between s and the first char of x
if (*i == *x_begin) {
//-----------^
// Code breaks here. Hovering above shows: 0x008ff000 <Bad Ptr>
// assign s's matching char
match = i;
// if x's lenght is 1 return match
if (len_x == 1) return match;
// define new pointer to the next element of s
char *i_next = i + 1;
// traverse the rest of x
for (char* j = x_begin + 1; j != x_end; ++j) {
// if there is even one mismatch brake loop and continue traversing s
if (*i_next != *j) break;
// if the rest of x matches the rest of s, switch to full_match
else if (j == x_end - 1) full_match = true;
// increment x
++i_next;
}
// when x traversed and there is full_match, return the first matching char
if (full_match) return match;
}
}
// return nullptr to indicate no match
return nullptr;
}
//====================================================
int main () {
try {
char* source = "abcde\0";
char* target = "c\0";
char *match_found = find(source, target);
if(match_found) std::cout << *match_found << '\n';
} catch (std::exception &e) {
std::cerr << e.what() << std::endl;
getchar();
}
getchar();
}
Why is the pointer char* i not initialized to s_begin? What am I doing wrong?

Answer 1

Your loop condition is wrong. What you have is an infinite loop:
for (char* i = s_begin; s_begin != s_end; ++i)
Since s_begin will never equal s_end i ends up incrementing outside of the string. Change it to:
for (char* i = s_begin; i != s_end; ++i)