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diff --git a/libs/algorithm/string/doc/usage.xml b/libs/algorithm/string/doc/usage.xml new file mode 100644 index 000000000..4d14ee16c --- /dev/null +++ b/libs/algorithm/string/doc/usage.xml @@ -0,0 +1,366 @@ +<?xml version="1.0" encoding="utf-8"?> +<!DOCTYPE library PUBLIC "-//Boost//DTD BoostBook XML V1.0//EN" +"http://www.boost.org/tools/boostbook/dtd/boostbook.dtd"> + + +<!-- Copyright (c) 2002-2006 Pavol Droba. + Subject to the Boost Software License, Version 1.0. + (See accompanying file LICENSE_1_0.txt or http://www.boost.org/LICENSE_1_0.txt) +--> + + +<section id="string_algo.usage" last-revision="$Date: 2013-05-22 08:10:49 -0700 (Wed, 22 May 2013) $"> + <title>Usage</title> + + <using-namespace name="boost"/> + <using-namespace name="boost::algorithm"/> + + + <section> + <title>First Example</title> + + <para> + Using the algorithms is straightforward. Let us have a look at the first example: + </para> + <programlisting> + #include <boost/algorithm/string.hpp> + using namespace std; + using namespace boost; + + // ... + + string str1(" hello world! "); + to_upper(str1); // str1 == " HELLO WORLD! " + trim(str1); // str1 == "HELLO WORLD!" + + string str2= + to_lower_copy( + ireplace_first_copy( + str1,"hello","goodbye")); // str2 == "goodbye world!" + </programlisting> + <para> + This example converts str1 to upper case and trims spaces from the start and the end + of the string. str2 is then created as a copy of str1 with "hello" replaced with "goodbye". + This example demonstrates several important concepts used in the library: + </para> + <itemizedlist> + <listitem> + <para><emphasis role="bold">Container parameters:</emphasis> + Unlike in the STL algorithms, parameters are not specified only in the form + of iterators. The STL convention allows for great flexibility, + but it has several limitations. It is not possible to <emphasis>stack</emphasis> algorithms together, + because a container is passed in two parameters. Therefore it is not possible to use + a return value from another algorithm. It is considerably easier to write + <code>to_lower(str1)</code>, than <code>to_lower(str1.begin(), str1.end())</code>. + </para> + <para> + The magic of <ulink url="../../libs/range/index.html">Boost.Range</ulink> + provides a uniform way of handling different string types. + If there is a need to pass a pair of iterators, + <ulink url="../../libs/range/doc/html/range/reference/utilities/iterator_range.html"><code>boost::iterator_range</code></ulink> + can be used to package iterators into a structure with a compatible interface. + </para> + </listitem> + <listitem> + <para><emphasis role="bold">Copy vs. Mutable:</emphasis> + Many algorithms in the library are performing a transformation of the input. + The transformation can be done in-place, mutating the input sequence, or a copy + of the transformed input can be created, leaving the input intact. None of + these possibilities is superior to the other one and both have different + advantages and disadvantages. For this reason, both are provided with the library. + </para> + </listitem> + <listitem> + <para><emphasis role="bold">Algorithm stacking:</emphasis> + Copy versions return a transformed input as a result, thus allow a simple chaining of + transformations within one expression (i.e. one can write <code>trim_copy(to_upper_copy(s))</code>). + Mutable versions have <code>void</code> return, to avoid misuse. + </para> + </listitem> + <listitem> + <para><emphasis role="bold">Naming:</emphasis> + Naming follows the conventions from the Standard C++ Library. If there is a + copy and a mutable version of the same algorithm, the mutable version has no suffix + and the copy version has the suffix <emphasis>_copy</emphasis>. + Some algorithms have the prefix <emphasis>i</emphasis> + (e.g. <functionname>ifind_first()</functionname>). + This prefix identifies that the algorithm works in a case-insensitive manner. + </para> + </listitem> + </itemizedlist> + <para> + To use the library, include the <headername>boost/algorithm/string.hpp</headername> header. + If the regex related functions are needed, include the + <headername>boost/algorithm/string_regex.hpp</headername> header. + </para> + </section> + <section> + <title>Case conversion</title> + + <para> + STL has a nice way of converting character case. Unfortunately, it works only + for a single character and we want to convert a string, + </para> + <programlisting> + string str1("HeLlO WoRld!"); + to_upper(str1); // str1=="HELLO WORLD!" + </programlisting> + <para> + <functionname>to_upper()</functionname> and <functionname>to_lower()</functionname> convert the case of + characters in a string using a specified locale. + </para> + <para> + For more information see the reference for <headername>boost/algorithm/string/case_conv.hpp</headername>. + </para> + </section> + <section> + <title>Predicates and Classification</title> + <para> + A part of the library deals with string related predicates. Consider this example: + </para> + <programlisting> + bool is_executable( string& filename ) + { + return + iends_with(filename, ".exe") || + iends_with(filename, ".com"); + } + + // ... + string str1("command.com"); + cout + << str1 + << (is_executable(str1)? "is": "is not") + << "an executable" + << endl; // prints "command.com is an executable" + + //.. + char text1[]="hello"; + cout + << text1 + << (all( text1, is_lower() )? " is": " is not") + << " written in the lower case" + << endl; // prints "hello is written in the lower case" + </programlisting> + <para> + The predicates determine whether if a substring is contained in the input string + under various conditions. The conditions are: a string starts with the substring, + ends with the substring, + simply contains the substring or if both strings are equal. See the reference for + <headername>boost/algorithm/string/predicate.hpp</headername> for more details. + </para> + <para> + Note that if we had used "hello world" as the input to the test, it would have + output "hello world is not written in the lower case" because the space in the + input string is not a lower case letter. + </para> + <para> + In addition the algorithm <functionname>all()</functionname> checks + all elements of a container to satisfy a condition specified by a predicate. + This predicate can be any unary predicate, but the library provides a bunch of + useful string-related predicates and combinators ready for use. + These are located in the <headername>boost/algorithm/string/classification.hpp</headername> header. + Classification predicates can be combined using logical combinators to form + a more complex expressions. For example: <code>is_from_range('a','z') || is_digit()</code> + </para> + </section> + <section> + <title>Trimming</title> + + <para> + When parsing the input from a user, strings often have unwanted leading or trailing + characters. To get rid of them, we need trim functions: + </para> + <programlisting> + string str1=" hello world! "; + string str2=trim_left_copy(str1); // str2 == "hello world! " + string str3=trim_right_copy(str1); // str3 == " hello world!" + trim(str1); // str1 == "hello world!" + + string phone="00423333444"; + // remove leading 0 from the phone number + trim_left_if(phone,is_any_of("0")); // phone == "423333444" + </programlisting> + <para> + It is possible to trim the spaces on the right, on the left or on both sides of a string. + And for those cases when there is a need to remove something else than blank space, there + are <emphasis>_if</emphasis> variants. Using these, a user can specify a functor which will + select the <emphasis>space</emphasis> to be removed. It is possible to use classification + predicates like <functionname>is_digit()</functionname> mentioned in the previous paragraph. + See the reference for the <headername>boost/algorithm/string/trim.hpp</headername>. + </para> + </section> + <section> + <title>Find algorithms</title> + + <para> + The library contains a set of find algorithms. Here is an example: + </para> + <programlisting> + char text[]="hello dolly!"; + iterator_range<char*> result=find_last(text,"ll"); + + transform( result.begin(), result.end(), result.begin(), bind2nd(plus<char>(), 1) ); + // text = "hello dommy!" + + to_upper(result); // text == "hello doMMy!" + + // iterator_range is convertible to bool + if(find_first(text, "dolly")) + { + cout << "Dolly is there" << endl; + } + </programlisting> + <para> + We have used <functionname>find_last()</functionname> to search the <code>text</code> for "ll". + The result is given in the <ulink url="../../libs/range/doc/html/range/reference/utilities/iterator_range.html"><code>boost::iterator_range</code></ulink>. + This range delimits the + part of the input which satisfies the find criteria. In our example it is the last occurrence of "ll". + + As we can see, input of the <functionname>find_last()</functionname> algorithm can be also + char[] because this type is supported by + <ulink url="../../libs/range/index.html">Boost.Range</ulink>. + + The following lines transform the result. Notice that + <ulink url="../../libs/range/doc/html/range/reference/utilities/iterator_range.html"><code>boost::iterator_range</code></ulink> has familiar + <code>begin()</code> and <code>end()</code> methods, so it can be used like any other STL container. + Also it is convertible to bool therefore it is easy to use find algorithms for a simple containment checking. + </para> + <para> + Find algorithms are located in <headername>boost/algorithm/string/find.hpp</headername>. + </para> + </section> + <section> + <title>Replace Algorithms</title> + <para> + Find algorithms can be used for searching for a specific part of string. Replace goes one step + further. After a matching part is found, it is substituted with something else. The substitution is computed + from the original, using some transformation. + </para> + <programlisting> + string str1="Hello Dolly, Hello World!" + replace_first(str1, "Dolly", "Jane"); // str1 == "Hello Jane, Hello World!" + replace_last(str1, "Hello", "Goodbye"); // str1 == "Hello Jane, Goodbye World!" + erase_all(str1, " "); // str1 == "HelloJane,GoodbyeWorld!" + erase_head(str1, 6); // str1 == "Jane,GoodbyeWorld!" + </programlisting> + <para> + For the complete list of replace and erase functions see the + <link linkend="string_algo.reference">reference</link>. + There is a lot of predefined function for common usage, however, the library allows you to + define a custom <code>replace()</code> that suits a specific need. There is a generic <functionname>find_format()</functionname> + function which takes two parameters. + The first one is a <link linkend="string_algo.finder_concept">Finder</link> object, the second one is + a <link linkend="string_algo.formatter_concept">Formatter</link> object. + The Finder object is a functor which performs the searching for the replacement part. The Formatter object + takes the result of the Finder (usually a reference to the found substring) and creates a + substitute for it. Replace algorithm puts these two together and makes the desired substitution. + </para> + <para> + Check <headername>boost/algorithm/string/replace.hpp</headername>, <headername>boost/algorithm/string/erase.hpp</headername> and + <headername>boost/algorithm/string/find_format.hpp</headername> for reference. + </para> + </section> + <section> + <title>Find Iterator</title> + + <para> + An extension to find algorithms it the Find Iterator. Instead of searching for just a one part of a string, + the find iterator allows us to iterate over the substrings matching the specified criteria. + This facility is using the <link linkend="string_algo.finder_concept">Finder</link> to incrementally + search the string. + Dereferencing a find iterator yields an <ulink url="../../libs/range/doc/html/range/reference/utilities/iterator_range.html"><code>boost::iterator_range</code></ulink> + object, that delimits the current match. + </para> + <para> + There are two iterators provided <classname>find_iterator</classname> and + <classname>split_iterator</classname>. The former iterates over substrings that are found using the specified + Finder. The latter iterates over the gaps between these substrings. + </para> + <programlisting> + string str1("abc-*-ABC-*-aBc"); + // Find all 'abc' substrings (ignoring the case) + // Create a find_iterator + typedef find_iterator<string::iterator> string_find_iterator; + for(string_find_iterator It= + make_find_iterator(str1, first_finder("abc", is_iequal())); + It!=string_find_iterator(); + ++It) + { + cout << copy_range<std::string>(*It) << endl; + } + + // Output will be: + // abc + // ABC + // aBC + + typedef split_iterator<string::iterator> string_split_iterator; + for(string_split_iterator It= + make_split_iterator(str1, first_finder("-*-", is_iequal())); + It!=string_split_iterator(); + ++It) + { + cout << copy_range<std::string>(*It) << endl; + } + + // Output will be: + // abc + // ABC + // aBC + </programlisting> + <para> + Note that the find iterators have only one template parameter. It is the base iterator type. + The Finder is specified at runtime. This allows us to typedef a find iterator for + common string types and reuse it. Additionally make_*_iterator functions help + to construct a find iterator for a particular range. + </para> + <para> + See the reference in <headername>boost/algorithm/string/find_iterator.hpp</headername>. + </para> + </section> + <section> + <title>Split</title> + + <para> + Split algorithms are an extension to the find iterator for one common usage scenario. + These algorithms use a find iterator and store all matches into the provided + container. This container must be able to hold copies (e.g. <code>std::string</code>) or + references (e.g. <code>iterator_range</code>) of the extracted substrings. + </para> + <para> + Two algorithms are provided. <functionname>find_all()</functionname> finds all copies + of a string in the input. <functionname>split()</functionname> splits the input into parts. + </para> + + <programlisting> + string str1("hello abc-*-ABC-*-aBc goodbye"); + + typedef vector< iterator_range<string::iterator> > find_vector_type; + + find_vector_type FindVec; // #1: Search for separators + ifind_all( FindVec, str1, "abc" ); // FindVec == { [abc],[ABC],[aBc] } + + typedef vector< string > split_vector_type; + + split_vector_type SplitVec; // #2: Search for tokens + split( SplitVec, str1, is_any_of("-*"), token_compress_on ); // SplitVec == { "hello abc","ABC","aBc goodbye" } + </programlisting> + <para> + <code>[hello]</code> designates an <code>iterator_range</code> delimiting this substring. + </para> + <para> + First example show how to construct a container to hold references to all extracted + substrings. Algorithm <functionname>ifind_all()</functionname> puts into FindVec references + to all substrings that are in case-insensitive manner equal to "abc". + </para> + <para> + Second example uses <functionname>split()</functionname> to split string str1 into parts + separated by characters '-' or '*'. These parts are then put into the SplitVec. + It is possible to specify if adjacent separators are concatenated or not. + </para> + <para> + More information can be found in the reference: <headername>boost/algorithm/string/split.hpp</headername>. + </para> + </section> +</section> |