Boost.Regex官方手册：C++正则表达式库

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"C++ boost regex manual" Boost.Regex是C++编程语言中Boost库的一部分，由John Maddock创建并维护，旨在提供强大的正则表达式处理功能。该库的使用涵盖了从基本的文本匹配到复杂的模式查找和替换，且遵循了多种正则表达式语法标准，包括Perl和POSIX。在配置Boost.Regex时，开发者需要考虑编译器的设置，以确保与库的兼容性。这部分涉及如何选择合适的编译器选项，以支持Boost库和Boost.Regex的功能。此外，还需要根据项目需求选择合适的locale和traits类，以便处理不同语言环境下的文本。链接选项让开发者能够选择静态或动态链接Boost.Regex库，这会影响到最终可执行文件的大小和依赖性。算法的选择和调整则涉及到如何优化匹配性能，包括匹配策略和内存使用。构建和安装Boost库，特别是Boost.Regex部分，通常需要按照官方提供的指南进行。这包括下载Boost源码、配置构建系统（如使用bjam或CMake）、编译和安装库到目标目录。 Boost.Regex提供了丰富的正则表达式语法，包括Perl风格的正则表达式和两种POSIX（Portable Operating System Interface）标准——基本和扩展模式。这些语法允许开发者构建复杂表达式以匹配和捕获文本中的模式。正则表达式中的标记子表达式和捕获可以用于提取匹配的特定部分。部分匹配功能允许在不完全符合整个模式的情况下找到可能的匹配项。理解这些概念对于有效地使用Boost.Regex至关重要。 Boost.Regex支持Unicode字符集，这意味着可以处理多种语言和特殊字符。同时，库还提供了对字符类的支持，包括通用字符类和特定于Unicode的字符类。Collating names、digraphs以及POSIX符号名称等高级特性使得处理文本更加灵活。搜索和替换功能的格式字符串语法借鉴了Perl和Sed工具的格式，同时Boost还提供了一种扩展的格式字符串语法，以满足更复杂的替换需求。 `basic_regex`是Boost.Regex库中的核心类，用于存储和操作正则表达式。它包含了各种构造函数、成员函数和模板，允许用户构建、编译和执行正则表达式。 "C++ boost regex manual"是开发者学习和使用Boost库中的正则表达式功能的详细指南，覆盖了从基础到高级的各个方面，对于任何想要在C++项目中利用正则表达式的开发者来说，都是宝贵的参考资料。

#include <iostream>

#include <fstream>

#include <sstream>

#include <string>

#include <boost/regex.hpp>

// match some kind of html tag:

boost::regex e("<[^>]*>");

// count how many:

unsigned int tags = 0;

void search(std::istream& is)

{

// buffer we'll be searching in:

char buf[4096];

// saved position of end of partial match:

const char* next_pos = buf + sizeof(buf);

// flag to indicate whether there is more input to come:

bool have_more = true;

while(have_more)

{

// how much do we copy forward from last try:

unsigned leftover = (buf + sizeof(buf)) - next_pos;

// and how much is left to fill:

unsigned size = next_pos - buf;

// copy forward whatever we have left:

std::memmove(buf, next_pos, leftover);

// fill the rest from the stream:

is.read(buf + leftover, size);

unsigned read = is.gcount();

// check to see if we've run out of text:

have_more = read == size;

// reset next_pos:

next_pos = buf + sizeof(buf);

// and then iterate:

boost::cregex_iterator a(

buf,

buf + read + leftover,

boost::match_default | boost::match_partial);

boost::cregex_iterator b;

while(a != b)

{

if((*a)[0].matched == false)

{

// Partial match, save position and break:

next_pos = (*a)[0].first;

break;

}

else

{

// full match:

++tags;

}

Boost.Regex

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(?:abc)?? has exactly the same effect.

Character sets

A character set is a bracket-expression starting with [ and ending with ], it deﬁnes a set of characters, and matches any single

character that is a member of that set.

A bracket expression may contain any combination of the following:

Single characters

For example [abc], will match any of the characters 'a', 'b', or 'c'.

Character ranges

For example [a-c] will match any single character in the range 'a' to 'c'. By default, for Perl regular expressions, a character x is

within the range y to z, if the code point of the character lies within the codepoints of the endpoints of the range. Alternatively, if

you set the collate ﬂag when constructing the regular expression, then ranges are locale sensitive.

Negation

If the bracket-expression begins with the ^ character, then it matches the complement of the characters it contains, for example

[^a-c] matches any character that is not in the range a-c.

Character classes

An expression of the form [[:name:]] matches the named character class "name", for example [[:lower:]] matches any lower

case character. See character class names.

Collating Elements

An expression of the form [[.col.] matches the collating element col. A collating element is any single character, or any sequence

of characters that collates as a single unit. Collating elements may also be used as the end point of a range, for example: [[.ae.]-

c] matches the character sequence "ae", plus any single character in the range "ae"-c, assuming that "ae" is treated as a single collating

element in the current locale.

As an extension, a collating element may also be speciﬁed via it's symbolic name, for example:

[[.NUL.]]

matches a \0 character.

Equivalence classes

An expression of the form [[=col=]], matches any character or collating element whose primary sort key is the same as that for

collating element col, as with collating elements the name col may be a symbolic name. A primary sort key is one that ignores case,

accentation, or locale-speciﬁc tailorings; so for example [[=a=]] matches any of the characters: a, À, Á, Â, Ã, Ä, Å, A, à, á, â, ã,

ä and å. Unfortunately implementation of this is reliant on the platform's collation and localisation support; this feature can not be

relied upon to work portably across all platforms, or even all locales on one platform.

Escaped Characters

All the escape sequences that match a single character, or a single character class are permitted within a character class deﬁnition.

For example [\[\]] would match either of [ or ] while [\W\d] would match any character that is either a "digit", or is not a "word"

character.

Combinations

All of the above can be combined in one character set declaration, for example: [[:digit:]a-c[.NUL.]].

Boost.Regex

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