C ++打印阵列

Question

I'm working on linear and quadratic probing hash table implementation in C++. In Hash.cpp, I have a working linearProb(int key) and quadProb functions. If I call them separately through main.hpp, it prints out correct hash table, but I want to see the result of both linear and quadratic tables when I compile.

This is my linearProb (quadProb looks similar)

void Hash::linearProb(int key){

    int i, count = 0;
    Hash h;

   //if it is empty, place it there
   if (a[key % tableSize] == -1)
    a[key % tableSize] = key;

   else{
       i = 0;

       //until finding an empty slot, but don't loop around
       while (i < tableSize && a[i] != -1){
                count++;
                i++;
       }

       if(count == tableSize){
           cout<<key<<" could not be inserted in the table\n";
           exit(1);
       }
       //when there's a collision increase i by 1 until finding empty slot
       for(i = (key % tableSize+1) % tableSize; i <tableSize; i++){
           if(a[i] == -1){
               a[i] = key;
               break;
           }
       }
   }
}

and I also have print() in Hash.cpp

void Hash::print(){
    int i;

    //cout<<"Hash Table with Linear Probing"<<endl;
    cout<<"\n Result Hash Table: "<<endl;

    for(i = 0; i < tableSize; i++){
        cout<<"\n"<<i;
        if(a[i] != -1){
        cout<<" "<< a[i];
        }
    }
    cout<<"\n";
}

If I call it in main.cpp like this

int main(){
    int key;
    Hash h;

    //take in .txt file
    std::fstream file;
    file.open("keys.txt");

    while(!file.eof()){
        file >> key;

        if(key != -1){
        h.linearProb(key);
        //h.quadProb(key);
        }
    }

    file.close();

    if(key == -1){
        h.print();
    }
}

I can see that my probing works, but notice that I commented out quadProb in order to test linearProb. I want to print out both tables at the same time. In order to do that, I attempted to call print() in each probing function instead of calling it from main.

This is what I tried. I changed main() to

while(!file.eof()){
    file >> key;

    h.linearProb(key);
    //h.quadProb(key);        
}

file.close();

and added to linearProb(int key)

void Hash::linearProb(int key){
    int i, count = 0;
    Hash h;

    if(key == -1){
        h.print();
        exit(1);
    }
}

But this only print out 0~9 without a[i]. When I tested what a[i] is when it enters print(), and it gives me all i value has a[i] of -1, which leads to not printing out anything. I'm really confused why this is happening. Why is print() not getting correct a[i] even though it worked when I called print() through main?

Answer 1

In your "print from probe function", you print an empty hash h declared in the function. You should drop that Hash h; and just call print() instead of h.print() .

This is a nice problem that a debugger can help you with. When breaking in that branch, it would show an empty h , while in main, h would be filled.