SEI PowerPoint Presentation for LiuHui, Object-Oriented Programming for C++, 2 nd Edition Copyright...

PowerPoint Presentation for LiuHui, Object-Oriented Programming for C++, 2nd Edition

Copyright 2007 © SEI, All rights reserved.1 - 32 SEI

Object-Oriented Object-Oriented ProgrammingProgramming



Chapter2 From C to C++Chapter2 From C to C++

2.1 Namespaces2.2 Introduction to C++ Input/Output2.3 Files2.4 C++ Features2.5 The Type string



2.1 Namespaces2.1 Namespaces

名空间

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NamespacesC++ provides namespaces to prevent name conflicts.

namespace mfc { int inflag; // …} // no closing semicolon requirednamespace owl { int inflag; // …} // no closing semicolon required

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Namespaces – scope resolution operator

The scope resolution operator :: occurs between the namespaces name and the variable.

mfc :: inflag = 3; // mfc’s inflagowl :: inflag = -823; // owl’s inflag

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Namespaces – using declaration

A using declaration （using声明） applies a single item in the namespace.namespace mfc { int inflag; void g(int); //…}

using mfc :: inflag;inflag = 1;mfc::g(6);

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Namespaces – using directiveUsing directive （using 指示） is equivalent to a using declaration for each item in a namespace.using namespace mfc;

inflag = 21;g(-66);owl::inflag = 341;

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Namespaces - stdC++’s std namespaces includes all of the standard libraries.

#include <iostream>using namespace std;

int main() { cout << "C++: one small step for the program, \n" << "one giant leap for the programmer\n"; return 0;}

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Conversion of C HeaderThe definitions, declarations, and so on in nonstandard C++ “.h” headers typically are not placed in namespaces.

The standard C header files have been renamed: .h is dropped and a c is prefixed.

stdlib.h cstdlibstdio.h cstdioctype.h cctype…



2.2 Introduction to C++ 2.2 Introduction to C++ Input/OutputInput/Output

C++ Input/Output – Manipulators （自己看）

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C++ Input/OutputIn C++, input/output is treated as a stream of consecutive(连续的 ) bytes.Thus C++ input/output is called stream input/output.

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C++ Input/OutputThe header iostream must be included to use C++ standard input/output.

cin: the standard inputcout: the standard output (buffered)cerr: the standard error (not buffered)

Two Operators, both operators recognize the data type supplied, so no format string (like that required for printf/scanf) is necessary.

>>: used for input<<: used for output

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C++ Input/Outputoperator >> and << recognize the data type supplied, so no format string is necessary.The default action of the input operator >> is to skip white space before reading the next input item, even if the variable is of type char.

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C++ Input/Output#include <iostream>using namespace std;int main() { int val, sum = 0; cout << "Enter next number: "; while( cin >> val ) { sum += val; cout << "Enter next number: "; } cout << "Sum of all values: " << sum << '\n'; return 0;}

if a value is read into val, cin >> val is true; otherwise, false.



2.3 Files2.3 Files

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FilesThe header file fstream must be included to use files.

ifstream: to read from a fileofstream: to write to a file>>: used to file read<<: used to file write

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Files#include <fstream>using namespace std;const int cutoff = 6000;const float rate1 = 0.3;const float rate2 = 0.6;int main() { ifstream infile; ofstream outfile; int income, tax; infile.open( "income.in" ); outfile.open( "tax.out" ); while ( infile >> income ) { if ( income < cutoff ) tax = rate1 * income; else tax = rate2 * income; outfile << "Income = " << income << " greenbacks\n" << "Tax = " << tax << " greenbacks\n"; } infile.close(); outfile.close(); return 0;}

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Files – Testing Whether Files Are Open

After opening a file, it is a good idea to check whether the file was successfully opened.

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Files - Testing Whether Files Are Open

#include <fstream>#include <iostream>using namespace std;const int cutoff = 6000;const float rate1 = 0.3;const float rate2 = 0.6;int main() { ifstream infile; ofstream outfile; int income, tax; infile.open( "income.in" ); if (!infile) { cerr << " Unable to open incom.in!\n "; exit(0); } outfile.open("tax.out" ); if (!outfile) { cerr << " Unable to open tax.out!\n "; exit(0); } //… infile.close(); outfile.close(); return 0;}



2.4 C++ Features2.4 C++ Features

Casts （类型转换，不用看）Constants （自己看）The Data Type boolEnumerated Types （自己看）Defining variables （自己看）Structures

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C++ Features – The Data Type bool

In C, true is represented by nonzero, and false by zero.C++ added the integer type bool to represent the boolean values true and false.

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C++ Features – Structures C++ has modified C’s version of structures.In addition to data members, in C++ a struct can contain functions.在 C++ 中，结构被看成是一种特殊的类。（以后详细介绍）



2.5 The Type string2.5 The Type string

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The Type stringC++ furnishes the type string as an alternative to C’s null-terminated arrays of char.By using string, the programmer does not have to be concerned about storage allocation or about handling the annoying null terminator.

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The Type string功能 String 中的方法举例

String Length

length() string s1; int size = s1.length();

Output Strings

cout<< string s1 = "abcd"; cout << s1 ;

Input Strings

cin>> string s1; cin >> s1;

Assignment = string s1, s2; s1 = "abcd"; s2 = s1;

Concatenation

+ string s1 = "abcd", s2 = "efg";string s3 = s1 + s2;

Modify String

erase 、 insert 、replace 、 swap

Extract substring

substr string s1 = "abcdergrehj";string s2 = s1.substr(4,6);

Searching findComparing == 、 != 、 < 、 <= 、> 、 >=

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The Type string - erase

#include <iostream>#include <string>using namespace std;

int main() { string s = "Ray_Dennis+Steckler"; s.erase(4, 7); // 从第 4 个字符开始连续删除 7 个字符 (Ray_Steckler) cout << s << '\n'; s.erase(4); // 删除从第 4 个字符开始的所有字符 (Ray_) cout << s << '\n'; return 0;}

The function erase removes a substring from a string.

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The Type string - insertThe function insert inserts a string at specified position.#include <iostream>#include <string>using namespace std;

int main() { string s1 = "Ray Steckler"; string s2 = "Dennis "; s1.insert(4, s2); // 将字符串 s2 插入到字符串 s1 的第 4 个字符之后 cout << s1 << '\n'; cout << s2 << '\n'; return 0;}

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The Type string - replaceThe function replace replaces a substring with a specified string.

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The Type string - replace#include <iostream>#include <string>using namespace std;

int main() { string s1 = "Ray Dennis Steckler"; string s2 = "Fran"; s1.replace(4, 6, s2); // 用字符串 s2 替换字符串 s1 中从第 4 个字符

// 开始的连续 6 个字符 cout << s1 << '\n'; cout << s2 << '\n'; return 0;}

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The Type string - swap#include <iostream>#include <string>using namespace std;

int main() { string s1 = "Ray Dennis Steckler"; string s2 = "Fran"; s1.swap(s2); // 将字符串 s1 和字符串 s2 的值互换 cout << s1 << '\n'; cout << s2 << '\n'; return 0;}

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The Type string - findThe function find is used to search a string for a substring.#include <iostream>

#include <string>using namespace std;int main() { string s1 = "Ray Dennis Steckler"; string s2 = "Dennis"; int f = s1.find(s2); // 字符串 s1 中是否出现了字符串 s2 if ( f < s1.length() ) cout << "Found at index: " << f << '\n'; else cout << "Not found\n"; return 0;}

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