精通C++：47个工程难题与编程解决方案

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"《卓越C++：47个工程谜题、编程问题与解决方案》是一本由Herb Sutter所著的图书，由Addison-Wesley出版社于1999年11月出版。本书的ISBN号码为0-201-61562-2，共240页。作者通过实例展示了如何在标准C++中进行稳健的软件工程实践。如果你热爱解决棘手的C++问题并追求编写高效且可扩展的代码，这本书将是一个极好的挑战。书中包含了47个精心挑选的工程谜题和编程问题，这些题目源于互联网新闻组comp.lang.c++.moderated上广受欢迎的"每周编程大师"特色栏目。作者对这些问题进行了扩展和更新，确保它们符合ISO/ANSI C++官方标准。每个问题根据难度分级，旨在揭示常见的编程错误或设计上的细微考虑。书中的挑战鼓励读者自行尝试解答，然后作者会深入剖析代码，揭示问题所在，并展示修正方法。《卓越C++》不仅提供了娱乐性，更重要的是它能提升你的C++技能，使你成为最顶尖的C++程序员。书中涉及的内容广泛，从基础到高级，旨在帮助读者提高程序设计技巧和理解C++的最佳实践。无论你是初学者还是经验丰富的开发者，这本书都将是你提升C++能力的宝贵资源，带你探索和解决那些看似复杂但富有教育意义的编程挑战。"

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Table of Contents

Exceptional C++: 47 Engineering Puzzles,

Programming Problems, and Solutions

Herb Sutter

Publisher

: Addison Wesley

Pub Date : November 18, 1999

ISBN

: 0-201-61562-2

Pages

: 240

Exceptional C++

shows by example how to go about sound software engineering in standard C++. Do

you enjoy solving thorny C++ problems and puzzles? Do you relish writing robust and extensible

code? Then take a few minutes and challenge yourself with some tough C++ design and programming

problems.

The puzzles and problems in

Exceptional C++

not only entertain, they will help you hone your skills to

become the sharpest C++ programmer you can be. Many of these problems are culled from the

famous Guru of the Week feature of the Internet newsgroup comp.lang.c++.moderated, expanded

and updated to conform to the official ISO/ANSI C++ Standard.

Each problem is rated according to difficulty and is designed to illustrate subtle programming mistakes

or design considerations. After you've had a chance to attempt a solution yourself, the book then

dissects the code, illustrates what went wrong, and shows how the problem can be fixed. Covering a

broad range of C++ topics, the problems and solutions address critical issues such as:

Generic programming and how to write reusable templates

Exception safety issues and techniques

Robust class design and inheritance

Compiler firewalls and the Pimpl Idiom

Name lookup, namespaces, and the Interface Principle

Memory management issues and techniques

Traps, pitfalls, and anti-idioms

Optimization

Try your skills against the C++ masters and come away with the insight and experience to create

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Item 1. Iterators

Difficulty: 7

Every programmer who uses the standard library has to be aware of these common and not-so-

common iterator mistakes. How many of them can you find?

The following program has at least four iterator-related problems. How many can you find?

int main()

{

vector<Date> e;

copy( istream_iterator<Date>( cin ),

istream_iterator<Date>(),

back_inserter( e ) );

vector<Date>::iterator first =

find( e.begin(), e.end(), "01/01/95" );

vector<Date>::iterator last =

find( e.begin(), e.end(), "12/31/95" );

*last = "12/30/95";

copy( first,

last,

ostream_iterator<Date>( cout, "\n" ) );

e.insert( --e.end(), TodaysDate() );

copy( first,

last,

ostream_iterator<Date>( cout, "\n" ) );

}

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Table of Contents

Exceptional C++: 47 Engineering Puzzles,

Programming Problems, and Solutions

Herb Sutter

Publisher

: Addison Wesley

Pub Date : November 18, 1999

ISBN

: 0-201-61562-2

Pages

: 240

Exceptional C++

shows by example how to go about sound software engineering in standard C++. Do

you enjoy solving thorny C++ problems and puzzles? Do you relish writing robust and extensible

code? Then take a few minutes and challenge yourself with some tough C++ design and programming

problems.

The puzzles and problems in

Exceptional C++

not only entertain, they will help you hone your skills to

become the sharpest C++ programmer you can be. Many of these problems are culled from the

famous Guru of the Week feature of the Internet newsgroup comp.lang.c++.moderated, expanded

and updated to conform to the official ISO/ANSI C++ Standard.

Each problem is rated according to difficulty and is designed to illustrate subtle programming mistakes

or design considerations. After you've had a chance to attempt a solution yourself, the book then

dissects the code, illustrates what went wrong, and shows how the problem can be fixed. Covering a

broad range of C++ topics, the problems and solutions address critical issues such as:

Generic programming and how to write reusable templates

Exception safety issues and techniques

Robust class design and inheritance

Compiler firewalls and the Pimpl Idiom

Name lookup, namespaces, and the Interface Principle

Memory management issues and techniques

Traps, pitfalls, and anti-idioms

Optimization

Try your skills against the C++ masters and come away with the insight and experience to create

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Solution

int main()

{

vector<Date> e;

copy( istream_iterator<Date>( cin ),

istream_iterator<Date>(),

back_inserter( e ) );

This is fine so far. The Date class writer provided an extractor function with the signature

operator>>( istream&, Date& ), which is what istream_iterator<Date> uses to read the

Dates from the

cin

stream. The

copy()

algorithm just stuffs the Dates into the vector.

vector<Date>::iterator first =

find( e.begin(), e.end(),

01/01/95

);

vector<Date>::iterator last =

find( e.begin(), e.end(),

12/31/95

);

*last = "12/30/95";

Error: This may be illegal, because last may be

e.end()

and therefore not a dereferenceable

iterator.

The

find()

algorithm returns its second argument (the end iterator of the range) if the value is not

found. In this case, if "12/31/95" is not in

, then last is equal to

e.end()

, which points to one-

past-the-end of the container and is not a valid iterator.

copy(

first,

last,

ostream_iterator<Date>( cout,

) );

Error: This may be illegal because [first,last) may not be a valid range; indeed, first may

actually be after last

For example, if "01/01/95" is not found in

but "12/31/95" is, then the iterator last will point to

something earlier in the collection (the Date object equal to "12/31/95") than does the iterator first

(one past the end). However,

copy()

requires that first must point to an earlier place in the same

collection as

last—that is, [first

last) must be a valid range.

Unless you're using a checked version of the standard library that can detect some of these problems

for you, the likely symptom if this happens will be a difficult-to-diagnose core dump during or

sometime after the

copy()

e.insert(--e.end()

, TodaysDate() );

First error: The expression "

--e.end()

" is likely to be illegal.

The reason is simple, if a little obscure: On popular implementations of the standard library,

vector<Date>::iterator is often simply a Date*, and the C++ language doesn't allow you to

modify temporaries of builtin type. For example, the following plain-jane code is also illegal:

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•

Table of Contents

Exceptional C++: 47 Engineering Puzzles,

Programming Problems, and Solutions

Herb Sutter

Publisher

: Addison Wesley

Pub Date : November 18, 1999

ISBN

: 0-201-61562-2

Pages

: 240

Exceptional C++

shows by example how to go about sound software engineering in standard C++. Do

you enjoy solving thorny C++ problems and puzzles? Do you relish writing robust and extensible

code? Then take a few minutes and challenge yourself with some tough C++ design and programming

problems.

The puzzles and problems in

Exceptional C++

not only entertain, they will help you hone your skills to

become the sharpest C++ programmer you can be. Many of these problems are culled from the

famous Guru of the Week feature of the Internet newsgroup comp.lang.c++.moderated, expanded

and updated to conform to the official ISO/ANSI C++ Standard.

Each problem is rated according to difficulty and is designed to illustrate subtle programming mistakes

or design considerations. After you've had a chance to attempt a solution yourself, the book then

dissects the code, illustrates what went wrong, and shows how the problem can be fixed. Covering a

broad range of C++ topics, the problems and solutions address critical issues such as:

Generic programming and how to write reusable templates

Exception safety issues and techniques

Robust class design and inheritance

Compiler firewalls and the Pimpl Idiom

Name lookup, namespaces, and the Interface Principle

Memory management issues and techniques

Traps, pitfalls, and anti-idioms

Optimization

Try your skills against the C++ masters and come away with the insight and experience to create

Date* f(); // function that returns a Date*

p = --f(); // error, but could be "f() - 1"

Fortunately, we know that vector<Date>::iterator is a random-access iterator, so there's no loss

of efficiency in writing this (more) correctly as:

e.insert( e.end() - 1, TodaysDate() );

Second error: Now you still have the other error, which is: If

is empty, any attempt to take "the

iterator before

e.end()

" (whether you spell that "

--e.end()

" or "

e.end()–1

") will not be a valid

iterator.

copy(

first,

last,

ostream_iterator<Date>( cout,

) );

}

Error:

first

and

last may not be valid iterators any more.

vector

grows in "chunks" so that it won't have to reallocate its buffer every time you insert

something into it. However, sometimes the

vector

will be full, and adding something will trigger a

reallocation.

Here, as a result of the e.insert() operation, the vector may or may not grow, which means its

memory may or may not move. Because of this uncertainty, we must consider any existing iterators

into that container to be invalidated. In this case, if the memory really did move, then the buggy

copy()

will again generally manifest as a difficult-to-diagnose core dump.

Guideline

Never dereference an invalid iterator.

To summarize: When using iterators, be aware of four main issues.

Valid values: Is the iterator dereferenceable? For example, writing "

*e.end()

" is always a

programming error.

Valid lifetimes: Is the iterator still valid when it's being used? Or has it been invalidated by some

operation since we obtained it?

Valid ranges: Is a pair of iterators a valid range? Is first really before (or equal to) last

? Do

both really point into the same container?

Illegal builtin manipulation: For example, is the code trying to modify a temporary of builtin

type, as in "

--e.end()

" above? (Fortunately, the compiler can often catch this kind of mistake

for you, and for iterators of class type, the library author will often choose to allow this sort of

thing for syntactic convenience.)

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Table of Contents

Exceptional C++: 47 Engineering Puzzles,

Programming Problems, and Solutions

Herb Sutter

Publisher

: Addison Wesley

Pub Date : November 18, 1999

ISBN

: 0-201-61562-2

Pages

: 240

Exceptional C++

shows by example how to go about sound software engineering in standard C++. Do

you enjoy solving thorny C++ problems and puzzles? Do you relish writing robust and extensible

code? Then take a few minutes and challenge yourself with some tough C++ design and programming

problems.

The puzzles and problems in

Exceptional C++

not only entertain, they will help you hone your skills to

become the sharpest C++ programmer you can be. Many of these problems are culled from the

famous Guru of the Week feature of the Internet newsgroup comp.lang.c++.moderated, expanded

and updated to conform to the official ISO/ANSI C++ Standard.

Each problem is rated according to difficulty and is designed to illustrate subtle programming mistakes

or design considerations. After you've had a chance to attempt a solution yourself, the book then

dissects the code, illustrates what went wrong, and shows how the problem can be fixed. Covering a

broad range of C++ topics, the problems and solutions address critical issues such as:

Generic programming and how to write reusable templates

Exception safety issues and techniques

Robust class design and inheritance

Compiler firewalls and the Pimpl Idiom

Name lookup, namespaces, and the Interface Principle

Memory management issues and techniques

Traps, pitfalls, and anti-idioms

Optimization

Try your skills against the C++ masters and come away with the insight and experience to create

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Item 2. Case-Insensitive Strings—Part 1

Difficulty: 7

So you want a case-insensitive string class? Your mission, should you choose to accept it, is to write

one.

This Item is composed of three related points.

What does "

case-insensitive

" mean?

Write a

ci_string

class that is identical to the standard std::string class but that is case-

insensitive in the same way as the commonly provided extension

stricmp()

[1]

ci_string

should be usable as follows:

[1]

The

stricmp()

case-insensitive string comparison function is not part of the C or C++

standards, but it is a common extension on many C and C++ compilers.

ci_string s( "AbCdE" );

// case insensitive

assert( s == "abcde" );

assert( s == "ABCDE" );

// still case-preserving, of course

assert( strcmp( s.c_str(), "AbCdE" ) == 0 );

assert( strcmp( s.c_str(), "abcde" ) != 0 );

Is making case sensitivity a property of the object a good idea?

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•

Table of Contents

Exceptional C++: 47 Engineering Puzzles,

Programming Problems, and Solutions

Herb Sutter

Publisher

: Addison Wesley

Pub Date : November 18, 1999

ISBN

: 0-201-61562-2

Pages

: 240

Exceptional C++

shows by example how to go about sound software engineering in standard C++. Do

you enjoy solving thorny C++ problems and puzzles? Do you relish writing robust and extensible

code? Then take a few minutes and challenge yourself with some tough C++ design and programming

problems.

The puzzles and problems in

Exceptional C++

not only entertain, they will help you hone your skills to

become the sharpest C++ programmer you can be. Many of these problems are culled from the

famous Guru of the Week feature of the Internet newsgroup comp.lang.c++.moderated, expanded

and updated to conform to the official ISO/ANSI C++ Standard.

Each problem is rated according to difficulty and is designed to illustrate subtle programming mistakes

or design considerations. After you've had a chance to attempt a solution yourself, the book then

dissects the code, illustrates what went wrong, and shows how the problem can be fixed. Covering a

broad range of C++ topics, the problems and solutions address critical issues such as:

Generic programming and how to write reusable templates

Exception safety issues and techniques

Robust class design and inheritance

Compiler firewalls and the Pimpl Idiom

Name lookup, namespaces, and the Interface Principle

Memory management issues and techniques

Traps, pitfalls, and anti-idioms

Optimization

Try your skills against the C++ masters and come away with the insight and experience to create

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Solution

The answers to the three questions are as follows.

What does "

case-insensitive

" mean?

What "

case-insensitive

" actually means depends entirely on your application and language. For

example, many languages do not have cases at all. For those that do, you still have to decide

whether you want accented characters to compare equal to unaccented characters, and so on.

This Item provides guidance on how to implement case-insensitivity for standard strings in

whatever sense applies to your situation.

Write a

ci_string

class that is identical to the standard std::string class but that is case-

insensitive in the same way as the commonly provided extension

stricmp()

The "how can I make a case-insensitive string?" question is so common that it probably

deserves its own FAQ—hence this Item.

Here's what we want to achieve:

ci_string s(

AbCdE

);

// case insensitive

assert( s ==

abcde

);

assert( s ==

ABCDE

);

// still case-preserving, of course

assert( strcmp( s.c_str(),

AbCdE

) == 0 );

assert( strcmp( s.c_str(),

abcde

) != 0 );

The key here is to understand what a

string

actually is in Standard C++. If you look in your

trusty

string

header, you'll see something like this:

typedef basic_string<char> string;

string

isn't really a class; it's a

typedef

of a template. In turn, the

basic_string<>

template is declared as follows, possibly with additional implementation-specific template

parameters:

template<class charT,

class traits = char_traits<charT>,

class Allocator = allocator<charT> >

class basic_string;

So "

string

" really means "basic_string<char, char_traits<char>, allocator<char>

," possibly with additional defaulted template parameters specific to the implementation you're

using. We don't need to worry about the

allocator

part, but the key here is the char_traits

part, because char_traits defines how characters interact—and compare!

So let's compare

string

basic_string supplies useful comparison functions that let you

compare whether one

string

is equal to another, less than another, and so on. These

string

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