C++ Primer 读书笔记 第七章

1. To invoke a function we use the call operator, which is a pair of parentheses. The operands to the call operator are the name of the function and a (possibly empty) comma-separated list of arguments.

#include <iostream>
using namespace std;

string::size_type find_char(const string &s, char c)
{
    string::size_type i = 0;
    while (i != s.size() && s[i] != c)
        ++i;
    return i;
}

bool is_sentence(const string &s)
{
    return (find_char(s, '.') == s.size() - 1);
}

int add(const int &i)
{
    return (i + 1);
}

int main()
{
    cout << (is_sentence("abc") ? "YES" : "NO") << endl;
    cout << add(8) << endl;
    int a[] = {1, 2, 3, 4, 5, 6};
    return 0;
}

2. A function may not return another function or a built-in array type.

#include <iostream>
using namespace std;

//It is wrong to return built-in array type
int[] return_arr()
{
    int arr[] = {1,2,3};
    return arr;
}
int main()
{
    int b[] = return_arr();
    return 0;
}

3. The compiler treats

void fcn(const int i);
void fcn(int i);

    as the same.

f(int *)
f(int *const)

    also treated as the same.

    Because the parameter is a copy of the passed value.

4. In C++ it is safer and more natural to use reference parameters. A reference must be initialized using an object of the same type as the reference. A nonconst reference may be bound only to nonconst object of exactly the same type.

5. There are three common programming techniques to ensure that a function stays within the bounds of its array arguments.

    Place a marker as the end of the array.

    C-style        void fun(int *a, int len) //len is the length of the array

    C++ style    void func(int *begin, int *end)

6. array as the parameter

void pirntValues(int *)  //this is commonly used
void printValues(int [])     
void printValues(int [10]) //10 is meaningless

void printValues(int (&arr)[10]) //parameter is a reference to an array; size of array is fixed

//for multidimensional array
void foo(int (*matrix)[10]) //10 must be specified


int *matrix[10]       // array of 10 pointers

7. When a function returns a reference type, the return value is not copied. Instead, the object itself is returned.

    Reference returns are lvalues

    It may be surprising to assign to the return of a function, but the return is a reference. As such, it is just a synonym for the element returned.

#include <iostream>
using namespace std;

int &larger(int &a, int &b)
{
    return a > b ? a : b;
}

int main()
{
    int a = 4;
    int b = 5;
    cout << larger(a, b) << endl;
    larger(a, b) = 10;
    cout << "a = " << a << "\tb = " << b << endl;
    return 0;
}

//output:
//5
//a = 4     b = 10

8. Put inline functions in header files. They should be defined in header files.

9. Whenever an inline function is added to or changed in a header file, every source file that uses that header must be recompiled.

    So we should be careful when we write Makefile.

10. Const member function -> The object which invokes this function will not be changed.

11. Default constructor

class Sales_item {
public:
    double avg_price() const;
    bool same_isbn(const Sales_item &rhs) const //A member function that is defined inside the class is implicitly treated as an inline function
        { return isbn == rhs.isbn; }
    Sales_item(): units_sold(0), revenue(0) { } //as isbn is string, it has its own default constructor, it will initialized as ""

private:
    std::string isbn;
    unsigned units_sold;
    double revenue;
};

12. Overloaded Functions -> Same name, different parameters.

    Although we cannot pass an integral value to a enum parameter, we can pass an enum to a parameter of integral type.

13. typedef bool (*comFcn) (const string &, const string &);

14. Returning a pointer to function.

int (*ff(int)) (int *, int);

ff(int) is a function returns int (*)(int *, int);

//use typedef
typedef int (*PF)(int *, int);
PF ff(int); //ff returns a pointer to function

 15. Two overloaded functions.

lookup(Account&)
lookup(const Account&)

//class member functions
Screen& display(ostream &os)
const Screen& display(ostream &os) const