Benchmark for IsStringMadeOf

[DllImport("utils.dll", BestFitMapping = true, CallingConvention = CallingConvention.Cdecl)]
public static extern bool MadeOf(char[] str, char[] from);

// 49 seconds
public static bool IsStringMadeOf(this string str, string from)
{
    if (str.Length > from.Length) return false;
    return MadeOf((str + "\0").ToCharArray(), (from + "\0").ToCharArray());
}


C side;

#include <string.h>

extern "C"  __declspec(dllexport) bool MadeOf(char str[], char from[])
{

    int len1 = strlen(str);
    int len2 = strlen(from);

    for(int i= 0; i<len1; i++)
    {
        bool isExists = false;
        for(int j= 0; j < len2; j++)
        {
            if(str[i] == from[j])
            {
            from[j] = '?';
            isExists = true;
            break;
            }
        }
        if(!isExists)
        {
            return false;
        }
    }
    return true;
}