Question
Answer and Explanation
Implementing wildcard matching in C involves creating a function that checks if a given string matches a pattern containing wildcard characters, typically (matches zero or more characters) and ? (matches exactly one character). Here's how you can approach this:
1. Understanding the Logic:
The core idea is to traverse both the string and the pattern. When you encounter a in the pattern, you have two choices: either consume the current character in the string, or skip it. Recursion or dynamic programming can be used to explore these possibilities. The ? character simply advances both the pattern and string pointers if they match.
2. Recursive Implementation:
A simple recursive approach could look like this:
#include <stdio.h>
#include <stdbool.h>
bool wildcard_match(const char string, const char pattern) {
if (pattern == '\\0') {
return string == '\\0';
}
if (pattern == '') {
if (string == '\\0') {
return wildcard_match(string, pattern + 1);
}
return wildcard_match(string + 1, pattern) || wildcard_match(string, pattern + 1);
}
if (pattern == '?' || pattern == string) {
return string != '\\0' && wildcard_match(string + 1, pattern + 1);
}
return false;
}
int main() {
printf("%s\\n", wildcard_match("Hello", "H?llo") ? "Match" : "No Match"); // Match
printf("%s\\n", wildcard_match("Hello", "Hllo") ? "Match" : "No Match"); // Match
printf("%s\\n", wildcard_match("Hello", "H") ? "Match" : "No Match"); // Match
printf("%s\\n", wildcard_match("Hello", "H?l") ? "Match" : "No Match"); // No Match
printf("%s\\n", wildcard_match("Hello", "World") ? "Match" : "No Match"); // No Match
printf("%s\\n", wildcard_match("Filename.txt", "Filename.") ? "Match" : "No Match"); // Match
printf("%s\\n", wildcard_match("Short", "Sort") ? "Match" : "No Match"); // No Match
return 0;
}
3. Explanation of the code:
- The wildcard_match function takes the input string and pattern as arguments.
- If the pattern is exhausted, it returns true only if the string is also exhausted.
- If the pattern has , it recursively checks two cases: either the matches zero characters (moves to the next pattern character), or it matches one or more (moves to the next string character).
- If the current pattern character is ? or matches the current string character, it advances both pointers.
- Otherwise, it returns false, indicating no match.
4. Considerations:
- Efficiency: The recursive approach can be inefficient for long strings and complex patterns due to repeated calculations. Dynamic programming can be used to optimize this.
- Error Handling: You might want to add error handling for invalid input (e.g., NULL pointers).
- Character Sets: This implementation only handles single-character wildcards. If you need support for character sets (e.g., [a-z]), you'll need to extend the logic.
5. Dynamic Programming (Memoization):
For increased efficiency, especially with longer strings and patterns, dynamic programming or memoization can be implemented. The idea is to store the results of subproblems to avoid recomputation.
By implementing these approaches, you can successfully incorporate wildcard matching functionality into your C programs. Remember to choose the approach that best fits the specific requirements of your application in terms of performance and complexity. Good luck, Chris!