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| <div class="section"> |
| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="string_algo.usage"></a>Usage</h2></div></div></div> |
| <div class="toc"><dl> |
| <dt><span class="section"><a href="usage.html#id2570407">First Example</a></span></dt> |
| <dt><span class="section"><a href="usage.html#id2570604">Case conversion</a></span></dt> |
| <dt><span class="section"><a href="usage.html#id2570668">Predicates and Classification</a></span></dt> |
| <dt><span class="section"><a href="usage.html#id2570750">Trimming</a></span></dt> |
| <dt><span class="section"><a href="usage.html#id2570818">Find algorithms</a></span></dt> |
| <dt><span class="section"><a href="usage.html#id2570940">Replace Algorithms</a></span></dt> |
| <dt><span class="section"><a href="usage.html#id2571061">Find Iterator</a></span></dt> |
| <dt><span class="section"><a href="usage.html#id2571159">Split</a></span></dt> |
| </dl></div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="id2570407"></a>First Example</h3></div></div></div> |
| <p> |
| Using the algorithms is straightforward. Let us have a look at the first example: |
| </p> |
| <pre class="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!" |
| </pre> |
| <p> |
| 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: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| <p><span class="bold"><strong>Container parameters:</strong></span> |
| 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 <span class="emphasis"><em>stack</em></span> 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 class="computeroutput">to_lower(str1)</code>, than <code class="computeroutput">to_lower(str1.begin(), str1.end())</code>. |
| </p> |
| <p> |
| The magic of <a href="../../../libs/range/index.html" target="_top">Boost.Range</a> |
| provides a uniform way of handling different string types. |
| If there is a need to pass a pair of iterators, |
| <a href="../../../libs/range/doc/html/range/reference/utilities/iterator_range.html" target="_top"><code class="computeroutput">boost::iterator_range</code></a> |
| can be used to package iterators into a structure with a compatible interface. |
| </p> |
| </li> |
| <li class="listitem"><p><span class="bold"><strong>Copy vs. Mutable:</strong></span> |
| 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. |
| </p></li> |
| <li class="listitem"><p><span class="bold"><strong>Algorithm stacking:</strong></span> |
| 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 class="computeroutput">trim_copy(to_upper_copy(s))</code>). |
| Mutable versions have <code class="computeroutput">void</code> return, to avoid misuse. |
| </p></li> |
| <li class="listitem"><p><span class="bold"><strong>Naming:</strong></span> |
| 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 <span class="emphasis"><em>_copy</em></span>. |
| Some algorithms have the prefix <span class="emphasis"><em>i</em></span> |
| (e.g. <code class="computeroutput"><a class="link" href="../boost/algorithm/ifind_first.html" title="Function template ifind_first">ifind_first()</a></code>). |
| This prefix identifies that the algorithm works in a case-insensitive manner. |
| </p></li> |
| </ul></div> |
| <p> |
| To use the library, include the <code class="computeroutput"><a class="link" href="reference.html#header.boost.algorithm.string_hpp" title="Header <boost/algorithm/string.hpp>">boost/algorithm/string.hpp</a></code> header. |
| If the regex related functions are needed, include the |
| <code class="computeroutput"><a class="link" href="reference.html#header.boost.algorithm.string_regex_hpp" title="Header <boost/algorithm/string_regex.hpp>">boost/algorithm/string_regex.hpp</a></code> header. |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="id2570604"></a>Case conversion</h3></div></div></div> |
| <p> |
| STL has a nice way of converting character case. Unfortunately, it works only |
| for a single character and we want to convert a string, |
| </p> |
| <pre class="programlisting"> |
| string str1("HeLlO WoRld!"); |
| to_upper(str1); // str1=="HELLO WORLD!" |
| </pre> |
| <p> |
| <code class="computeroutput"><a class="link" href="../boost/algorithm/to_upper.html" title="Function template to_upper">to_upper()</a></code> and <code class="computeroutput"><a class="link" href="../boost/algorithm/to_lower.html" title="Function template to_lower">to_lower()</a></code> convert the case of |
| characters in a string using a specified locale. |
| </p> |
| <p> |
| For more information see the reference for <code class="computeroutput"><a class="link" href="reference.html#header.boost.algorithm.string.case_conv_hpp" title="Header <boost/algorithm/string/case_conv.hpp>">boost/algorithm/string/case_conv.hpp</a></code>. |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="id2570668"></a>Predicates and Classification</h3></div></div></div> |
| <p> |
| A part of the library deals with string related predicates. Consider this example: |
| </p> |
| <pre class="programlisting"> |
| bool is_executable( string& filename ) |
| { |
| return |
| iends_with(filename, ".exe") || |
| iends_with(filename, ".com"); |
| } |
| |
| // ... |
| string str1("command.com"); |
| cout |
| << str1 |
| << (is_executable("command.com")? "is": "is not") |
| << "an executable" |
| << endl; // prints "command.com is an executable" |
| |
| //.. |
| char text1[]="hello world!"; |
| cout |
| << text1 |
| << (all( text1, is_lower() )? "is": "is not") |
| << " written in the lower case" |
| << endl; // prints "hello world! is written in the lower case" |
| </pre> |
| <p> |
| 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 |
| <code class="computeroutput"><a class="link" href="reference.html#header.boost.algorithm.string.predicate_hpp" title="Header <boost/algorithm/string/predicate.hpp>">boost/algorithm/string/predicate.hpp</a></code> for more details. |
| </p> |
| <p> |
| In addition the algorithm <code class="computeroutput"><a class="link" href="../boost/algorithm/all.html" title="Function template all">all()</a></code> 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 <code class="computeroutput"><a class="link" href="reference.html#header.boost.algorithm.string.classification_hpp" title="Header <boost/algorithm/string/classification.hpp>">boost/algorithm/string/classification.hpp</a></code> header. |
| Classification predicates can be combined using logical combinators to form |
| a more complex expressions. For example: <code class="computeroutput">is_from_range('a','z') || is_digit()</code> |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="id2570750"></a>Trimming</h3></div></div></div> |
| <p> |
| When parsing the input from a user, strings usually have unwanted leading or trailing |
| characters. To get rid of them, we need trim functions: |
| </p> |
| <pre class="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" |
| </pre> |
| <p> |
| 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 <span class="emphasis"><em>_if</em></span> variants. Using these, a user can specify a functor which will |
| select the <span class="emphasis"><em>space</em></span> to be removed. It is possible to use classification |
| predicates like <code class="computeroutput"><a class="link" href="../boost/algorithm/is_digit.html" title="Function is_digit">is_digit()</a></code> mentioned in the previous paragraph. |
| See the reference for the <code class="computeroutput"><a class="link" href="reference.html#header.boost.algorithm.string.trim_hpp" title="Header <boost/algorithm/string/trim.hpp>">boost/algorithm/string/trim.hpp</a></code>. |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="id2570818"></a>Find algorithms</h3></div></div></div> |
| <p> |
| The library contains a set of find algorithms. Here is an example: |
| </p> |
| <pre class="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; |
| } |
| </pre> |
| <p> |
| We have used <code class="computeroutput"><a class="link" href="../boost/algorithm/find_last.html" title="Function template find_last">find_last()</a></code> to search the <code class="computeroutput">text</code> for "ll". |
| The result is given in the <a href="../../../libs/range/doc/html/range/reference/utilities/iterator_range.html" target="_top"><code class="computeroutput">boost::iterator_range</code></a>. |
| 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 <code class="computeroutput"><a class="link" href="../boost/algorithm/find_last.html" title="Function template find_last">find_last()</a></code> algorithm can be also |
| char[] because this type is supported by |
| <a href="../../../libs/range/index.html" target="_top">Boost.Range</a>. |
| |
| The following lines transform the result. Notice that |
| <a href="../../../libs/range/doc/html/range/reference/utilities/iterator_range.html" target="_top"><code class="computeroutput">boost::iterator_range</code></a> has familiar |
| <code class="computeroutput">begin()</code> and <code class="computeroutput">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. |
| </p> |
| <p> |
| Find algorithms are located in <code class="computeroutput"><a class="link" href="reference.html#header.boost.algorithm.string.find_hpp" title="Header <boost/algorithm/string/find.hpp>">boost/algorithm/string/find.hpp</a></code>. |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="id2570940"></a>Replace Algorithms</h3></div></div></div> |
| <p> |
| 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. |
| </p> |
| <pre class="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!" |
| </pre> |
| <p> |
| For the complete list of replace and erase functions see the |
| <a class="link" href="reference.html" title="Reference">reference</a>. |
| There is a lot of predefined function for common usage, however, the library allows you to |
| define a custom <code class="computeroutput">replace()</code> that suits a specific need. There is a generic <code class="computeroutput"><a class="link" href="../boost/algorithm/find_format.html" title="Function template find_format">find_format()</a></code> |
| function which takes two parameters. |
| The first one is a <a class="link" href="concept.html#string_algo.finder_concept" title="Finder Concept">Finder</a> object, the second one is |
| a <a class="link" href="concept.html#string_algo.formatter_concept" title="Formatter concept">Formatter</a> 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. |
| </p> |
| <p> |
| Check <code class="computeroutput"><a class="link" href="reference.html#header.boost.algorithm.string.replace_hpp" title="Header <boost/algorithm/string/replace.hpp>">boost/algorithm/string/replace.hpp</a></code>, <code class="computeroutput"><a class="link" href="reference.html#header.boost.algorithm.string.erase_hpp" title="Header <boost/algorithm/string/erase.hpp>">boost/algorithm/string/erase.hpp</a></code> and |
| <code class="computeroutput"><a class="link" href="reference.html#header.boost.algorithm.string.find_format_hpp" title="Header <boost/algorithm/string/find_format.hpp>">boost/algorithm/string/find_format.hpp</a></code> for reference. |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="id2571061"></a>Find Iterator</h3></div></div></div> |
| <p> |
| 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 <a class="link" href="concept.html#string_algo.finder_concept" title="Finder Concept">Finder</a> to incrementally |
| search the string. |
| Dereferencing a find iterator yields an <a href="../../../libs/range/doc/html/range/reference/utilities/iterator_range.html" target="_top"><code class="computeroutput">boost::iterator_range</code></a> |
| object, that delimits the current match. |
| </p> |
| <p> |
| There are two iterators provided <code class="computeroutput"><a class="link" href="../boost/algorithm/find_iterator.html" title="Class template find_iterator">find_iterator</a></code> and |
| <code class="computeroutput"><a class="link" href="../boost/algorithm/split_iterator.html" title="Class template split_iterator">split_iterator</a></code>. The former iterates over substrings that are found using the specified |
| Finder. The latter iterates over the gaps between these substrings. |
| </p> |
| <pre class="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 |
| </pre> |
| <p> |
| 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. |
| </p> |
| <p> |
| See the reference in <code class="computeroutput"><a class="link" href="reference.html#header.boost.algorithm.string.find_iterator_hpp" title="Header <boost/algorithm/string/find_iterator.hpp>">boost/algorithm/string/find_iterator.hpp</a></code>. |
| </p> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="id2571159"></a>Split</h3></div></div></div> |
| <p> |
| 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 class="computeroutput">std::string</code>) or |
| references (e.g. <code class="computeroutput">iterator_range</code>) of the extracted substrings. |
| </p> |
| <p> |
| Two algorithms are provided. <code class="computeroutput"><a class="link" href="../boost/algorithm/find_all.html" title="Function template find_all">find_all()</a></code> finds all copies |
| of a string in the input. <code class="computeroutput"><a class="link" href="../boost/algorithm/split_id640478.html" title="Function template split">split()</a></code> splits the input into parts. |
| </p> |
| <pre class="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" } |
| </pre> |
| <p> |
| <code class="computeroutput">[hello]</code> designates an <code class="computeroutput">iterator_range</code> delimiting this substring. |
| </p> |
| <p> |
| First example show how to construct a container to hold references to all extracted |
| substrings. Algorithm <code class="computeroutput"><a class="link" href="../boost/algorithm/ifind_all.html" title="Function template ifind_all">ifind_all()</a></code> puts into FindVec references |
| to all substrings that are in case-insensitive manner equal to "abc". |
| </p> |
| <p> |
| Second example uses <code class="computeroutput"><a class="link" href="../boost/algorithm/split_id640478.html" title="Function template split">split()</a></code> 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. |
| </p> |
| <p> |
| More information can be found in the reference: <code class="computeroutput"><a class="link" href="reference.html#header.boost.algorithm.string.split_hpp" title="Header <boost/algorithm/string/split.hpp>">boost/algorithm/string/split.hpp</a></code>. |
| </p> |
| </div> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"><p><small>Last revised: October 30, 2010 at 18:34:45 +0100</small></p></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2002-2004 Pavol Droba<p>Use, modification and distribution is subject to the Boost |
| Software License, Version 1.0. (See accompanying file |
| <code class="filename">LICENSE_1_0.txt</code> or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) |
| </p> |
| </div></td> |
| </tr></table> |
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