因为平时经常遇到C++，以后的课程应该也免不了要用，学一下C++。

参考用书：C++ Primer Plus(Sixth Edition)，作者：Stephen Prata

This passage includes notes of Chapter 5,6 and 7. I’ll try to be make it simple and easy to read. Most content of these chapters are familiar to people who has learnt C. Also, I’ll only take down notes that are new or not familiar to me.

Chpt 5. Loops and Relational Expressions

cout.setf() function

Note that in express.cpp, we use cout.setf(ios_base::boolalpha);. This function call sets a flag that instructs cout to display the words true and false instead of 1 and 0.

For loop

C++ allows you to declare a variable in the initialization area of a for loop, which is not permitted in C:

for (int i = 0; i < 5; i++)
    ...

Building a Time-Delay loop

In the ctime header file(or the time.h in traditional C), a function called clock() returns the system time elapsed since a program started execution. Note that clock() does not return the time in seconds, however, and the type of its return value might be long, unsigned long or others based on your system.

ctime header file provides solutions to these problems. First, It defines a symbolic constant, CLOCKS_PER_SEC, that equals the number of system time units per second. So dividing the system time by this value yields seconds. Or you can multiply seconds by CLOCKS_PER_SEC to get time in the system units.

Second, ctime establishes clock_t as an alias for the clock() return type. This means you can declare a variable as type clock_t, and the compiler cnverts it to long or unsigned int or whatever is the proper type for your system.

Special Note on cin

When reading type char values, just as when reading other basic types, cin skips over spaces and new line characters. You can refer to Listing 5.16 textin1.cpp to see this.

The End-of-File(EOF) condition

When cin detects the EOF, it sets two bits(the eofbit and the failbit) to 1. You can use a member function named eof() to see whether the eofbit has been set; the call cin.eof() returns the bool value true or false based on whether EOF has been detected or not.

Similarly, the fail() member function returns true if either the eofbit or the failbit has been set to 1 and false otherwise.

Note that the eof() and fail() methods report the result of the most recent attempt to read; that is, they report on the past rather than look ahead. So a cin.eof() or cin.fail() test should always follow an attempt to read. You can refer to Listing 5.18 textin3.cpp for this.

bool value of cin

The istream class provides a function that can convert an istream object such as cin to a bool value. This conversion function is called when cin occurs in a location where a bool is expected, such as in the test condition of a while loop.

Chpt 6. Branching Statements and Logical Operators

The cctype Library of Character Functions

The cctype header file(ctype.h in the older style) holds several functions that simplify such tasks as determining whether a character is an uppercase letter or a digit or punctuation. For example, the isalpha(ch) function returns a nonzero if ch is a letter and zero value otherwise. Similarly, the ispunct(ch) function returns a true value only if ch is a punctuation character, such as a comma or a period.

Reading Mismatch Type into a Variable

Suppose you have the beneath lines in a program:

int n;
cin >> n;

If you enter, say, a word instead a number? Four things occur in such a mismatch:

• The value of n is left unchanged.
• The mismatched input is left in the input queue.
• An error flag is set in the cin object.
• The call to the cin method, if converted to type bool, returns false.

The fact that the method returns false means that you can use non-numeric input to terminate a number-reading loop. The fact that non-numeric input sats an error flag means that you have to reset the flag before the program can read more input. You can use the clear() method to reset the error flag, just use cin.clear().

Simple File I/O

File output is silimar to console output using cout. In file output:

• You must include the fstream header file.
• The fstream header file defines an ofstream class for handling output.
• You need to declare one or more ofstream variables, or objects, which you can name as you please, as long as you respect the usual naming conventions.
• You must account for the std namespace; for example, you can use the using directive or the std:: prefix for elements such as ofstream.
• You need to associate a specific ofstream object with a specific file; one way to do so is to use the open() method.
• When you’re finished with a file, you should use the close() method to close the file.
• You can use an ofstream object with the << operator to output a variety of data types.

Note that although the iostream header file provides a predefined ostream object called cout, you have to declare your own ofstream object, choosing a name for it and associating it with a file. Here’s how you declare such objects:

ofstream outFile;           // outFile an ofstream object
ofstream fout;           // fout an ofstream object

You may refer to Listing 6.15 outfile.cpp for usage of ofstream class.

Note that when you open an existing file for output, by default it is truncated to a length of zero bytes, so the contents are lost.

ifstream class is similarly designed. Note that is_open() method returns true if the file was successfully opened. You can use is_open() method to check whether a file was opened successfully:

ifstream inFile;
inFile.open("bowling.txt");
if (!inFile.is_open())
    exit(EXIT_FAILURE);

The exit() function is prototyped in the cstdlib header file, which also defines EXIT_FAILURE as an argument value used to communicate with the operating system. The exit() function terminates the program.