1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
|
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<title>Usage</title>
<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css">
<meta name="generator" content="DocBook XSL Stylesheets V1.76.1">
<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset">
<link rel="up" href="../string_algo.html" title="Chapter 27. Boost String Algorithms Library">
<link rel="prev" href="release_notes.html" title="Release Notes">
<link rel="next" href="quickref.html" title="Quick Reference">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<table cellpadding="2" width="100%"><tr>
<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td>
<td align="center"><a href="../../../index.html">Home</a></td>
<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td>
<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
<td align="center"><a href="../../../more/index.htm">More</a></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="release_notes.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../string_algo.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="quickref.html"><img src="../../../doc/src/images/next.png" alt="Next"></a>
</div>
<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#id3183270">First Example</a></span></dt>
<dt><span class="section"><a href="usage.html#id3183468">Case conversion</a></span></dt>
<dt><span class="section"><a href="usage.html#id3183534">Predicates and Classification</a></span></dt>
<dt><span class="section"><a href="usage.html#id3183616">Trimming</a></span></dt>
<dt><span class="section"><a href="usage.html#id3183685">Find algorithms</a></span></dt>
<dt><span class="section"><a href="usage.html#id3183806">Replace Algorithms</a></span></dt>
<dt><span class="section"><a href="usage.html#id3183933">Find Iterator</a></span></dt>
<dt><span class="section"><a href="usage.html#id3184031">Split</a></span></dt>
</dl></div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id3183270"></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="id3183468"></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="id3183534"></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="id3183616"></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="id3183685"></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="id3183806"></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="id3183933"></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="id3184031"></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_id820181.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_id820181.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>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="release_notes.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../string_algo.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="quickref.html"><img src="../../../doc/src/images/next.png" alt="Next"></a>
</div>
</body>
</html>
|
