Objective

Implement a function that searches a string for the first occurrence of a substring and returns a pointer to where it begins.

Steps

• For each position in haystack, try to match needle character by character starting there.
• On the first position where the whole needle matches, return a pointer to that position inside haystack.
• If needle never appears, return NULL.
• An empty needle matches at the very start: return haystack unchanged.
• Watch the restart: when a partial match fails, resume the search from the next character, not from where the partial match stopped, strstr("aaab", "aab") must still find "aab".
• Do not modify either input buffer.

Objective

Implement a function that searches a string for the first occurrence of a substring and returns a pointer to where it begins.

Steps

• For each position in haystack, try to match needle character by character starting there.
• On the first position where the whole needle matches, return a pointer to that position inside haystack.
• If needle never appears, return NULL.
• An empty needle matches at the very start: return haystack unchanged.
• Watch the restart: when a partial match fails, resume the search from the next character, not from where the partial match stopped, strstr("aaab", "aab") must still find "aab".
• Do not modify either input buffer.