Question

I need to implement something like my own file system. One operation would be the FindFirstFile. I need to check, if the caller passed something like ., sample*.cpp or so. My “file system” implementation provides the list of “files names” as a array of char*.

Is there any Windows function or any source code that implements this file name matching?

Answer 1

There are quite a few such functions around. Here’s a directory of various implementations, sorted into recursive and non-recursive, etc.

In case you don’t like the licensing there (or have trouble with the link, etc.) here’s one possible implementation of a matching algorithm that at least closely approximates what Windows uses:

#include <string.h>
#include <iostream>

bool match(char const *needle, char const *haystack) {
    for (; *needle != '\0'; ++needle) {
        switch (*needle) {
        case '?': 
            if (*haystack == '\0')
                return false;
            ++haystack;
            break;
        case '*': {
            if (needle[1] == '\0')
                return true;
            size_t max = strlen(haystack);
            for (size_t i = 0; i < max; i++)
                if (match(needle + 1, haystack + i))
                    return true;
            return false;
        }
        default:
            if (*haystack != *needle)
                return false;
            ++haystack;
        }
    }
    return *haystack == '\0';
}

#ifdef TEST
#define CATCH_CONFIG_MAIN

#include "catch.hpp"

TEST_CASE("Matching", "[match]") {
    REQUIRE(match("a", "a") == true);
    REQUIRE(match("a", "b") == false);
    REQUIRE(match("a*", "a") == true);
    REQUIRE(match("a?", "a") == false);
    REQUIRE(match("a?", "ab") == true);
    REQUIRE(match("a*b", "ab") == true);
    REQUIRE(match("a*b", "acb") == true);
    REQUIRE(match("a*b", "abc") == false);
    REQUIRE(match("*a*??????a?????????a???????????????", 
        "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa") == true);
}

#endif

Since there was a discussion of complexity of some of the other answers, I’ll note that I believe this has O(NM) complexity and O(M) storage use (where N is the size of the target string, and M is the size of the pattern).

With @masterxilo’s test pair:

"*a*??????*a*?????????a???????????????", "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"

…this finds a match in approximately 3 microseconds on my machine. That is a lot slower than a typical pattern–most of my other tests run in about 300 nanoseconds or so on this particular machine.

At the same time, @masterxilo’s code takes approximately 11 microseconds to run on the same machine, so this is still around 3 to 4 times faster (not to mention being somewhat smaller and simpler).