With this function in place, you can use the following statement to sort the books vector of Review objects in order of increasing rating values:
sort(books.begin(), books.end(), WorseThan);
Note that the WorseThan() function does a less complete job than operator<() of ordering Review objects. If two objects have the same title member, the operator<() function sorts by using the rating member. But if two objects have the same rating member, WorseThan() treats them as equivalent. The first kind of ordering is called
Listing 16.9 illustrates the use of these STL functions.
Listing 16.9. vect3.cpp
// vect3.cpp -- using STL functions
#include
#include
#include
#include
struct Review {
std::string title;
int rating;
};
bool operator<(const Review & r1, const Review & r2);
bool worseThan(const Review & r1, const Review & r2);
bool FillReview(Review & rr);
void ShowReview(const Review & rr);
int main()
{
using namespace std;
vector
Review temp;
while (FillReview(temp))
books.push_back(temp);
if (books.size() > 0)
{
cout << "Thank you. You entered the following "
<< books.size() << " ratings:\n"
<< "Rating\tBook\n";
for_each(books.begin(), books.end(), ShowReview);
sort(books.begin(), books.end());
cout << "Sorted by title:\nRating\tBook\n";
for_each(books.begin(), books.end(), ShowReview);
sort(books.begin(), books.end(), worseThan);
cout << "Sorted by rating:\nRating\tBook\n";
for_each(books.begin(), books.end(), ShowReview);
random_shuffle(books.begin(), books.end());
cout << "After shuffling:\nRating\tBook\n";
for_each(books.begin(), books.end(), ShowReview);
}
else
cout << "No entries. ";
cout << "Bye.\n";
return 0;
}
bool operator<(const Review & r1, const Review & r2)
{
if (r1.title < r2.title)
return true;
else if (r1.title == r2.title && r1.rating < r2.rating)
return true;
else
return false;
}
bool worseThan(const Review & r1, const Review & r2)
{
if (r1.rating < r2.rating)
return true;
else
return false;
}
bool FillReview(Review & rr)
{
std::cout << "Enter book title (quit to quit): ";
std::getline(std::cin,rr.title);
if (rr.title == "quit")
return false;
std::cout << "Enter book rating: ";
std::cin >> rr.rating;
if (!std::cin)
return false;
// get rid of rest of input line
while (std::cin.get() != '\n')
continue;
return true;
}
void ShowReview(const Review & rr)
{
std::cout << rr.rating << "\t" << rr.title << std::endl;
}
Here’s a sample run of the program in Listing 16.9:
Enter book title (quit to quit): The Cat Who Can Teach You Weight Loss
Enter book rating: 8
Enter book title (quit to quit): The Dogs of Dharma
Enter book rating: 6
Enter book title (quit to quit): The Wimps of Wonk
Enter book rating: 3
Enter book title (quit to quit): Farewell and Delete
Enter book rating: 7
Enter book title (quit to quit): quit
Thank you. You entered the following 4 ratings:
Rating Book
8 The Cat Who Can Teach You Weight Loss
6 The Dogs of Dharma
3 The Wimps of Wonk
7 Farewell and Delete
Sorted by title:
Rating Book
7 Farewell and Delete
8 The Cat Who Can Teach You Weight Loss
6 The Dogs of Dharma
3 The Wimps of Wonk
Sorted by rating:
Rating Book
3 The Wimps of Wonk
6 The Dogs of Dharma
7 Farewell and Delete
8 The Cat Who Can Teach You Weight Loss
After shuffling:
Rating Book
7 Farewell and Delete
3 The Wimps of Wonk
6 The Dogs of Dharma
8 The Cat Who Can Teach You Weight Loss
Bye.
The Range-Based for Loop (C++11)
The range-based for loop, mentioned in Chapter 5, “Loops and Relational Expressions,” is designed to work with the STL. To review, here’s the first example from Chapter 5:
double prices[5] = {4.99, 10.99, 6.87, 7.99, 8.49};
for (double x : prices)
cout << x << std::endl;
The contents of the parentheses for the for loop declare a variable of the type stored in a container and then the name of the container. Next, the body of the loop uses the named variable to access each container element in turn. Consider, for instance, this statement from Listing 16.9:
for_each(books.begin(), books.end(), ShowReview);
It can be replaced with the following range-based for loop:
for (auto x : books) ShowReview(x);
The compiler will use the type of books, which is vector
