Everything works fine, until it gets to the bottom on (void displayData()). I'm getting some kind of error saying, "the address of 'int getLength(int&)' will always evaluate as 'true'

#include <iostream>
using namespace std;

int getLength(int&);
int getWidth(int&);
double getArea(double lengthNum, double widthNum);
void displayData();

int main(){
    int length, width; 

    
    getLength(length);
    getWidth(width);
    getArea(length, width);
    displayData();
    
    system("pause");
    return 0;
}

int getLength(int& lengthValue)
{
    
    
    cout << "Enter the length: ";
    cin >> lengthValue;
    
    if (lengthValue < 0)
    {
        cout << "\nERROR: Enter a positive number.\n";
        cout << "Enter the length: ";
        cin >> lengthValue;
        cout << endl;
    }
    return lengthValue;
}

int getWidth(int& widthValue)
{
   
    
    cout << "Enter the width: ";
    cin >> widthValue;
    
    if (widthValue < 0)
    {
        cout << "\nERROR: Enter a positive number.\n";
        cout << "Enter the width: ";
        cin >> widthValue;
        cout << endl;
    }
    return widthValue;
}

double getArea(double lengthNum, double widthNum)
{
    return lengthNum * widthNum;
}
//ERROR in here please HELP....Thanks in advance :)!
void displayData()
{
   
    cout << "Rectangle Data\n";
    cout << "--------------\n";
    cout << "Length: " << getLength << endl;
    cout << "Width: " << getWidth << endl;
    cout << "Area: " << getArea << endl;
}