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| <TITLE>Example Function: Split a Line into Words</TITLE> |
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| <H2>12.3 Example Function: Split a Line into Words</H2> |
| <A NAME="idx240"><!></A> |
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| <P>In this section we illustrate the use of some of the <B><I><A HREF="../stdlibref/basic-string.html">string</A></I></B> functions by defining a function to split a line of text into individual words. We have already made use of this function in the concordance example program in <A HREF="9-3.html#933">Section 9.3.3</A>.</P> |
| <BLOCKQUOTE><HR><B> |
| NOTE -- The split function is in the concordance program in file concord.cpp. |
| </B><HR></BLOCKQUOTE> |
| <P>There are three arguments to this function. The first two are <B><I><A HREF="../stdlibref/basic-string.html">string</A></I></B>s, describing the line of text and the separators to be used to differentiate words, respectively. The third argument is a <B><I><A HREF="../stdlibref/list.html">list</A></I></B> of <B><I>string</I></B>s, used to return the individual words in the line.</P> |
| |
| <UL><PRE> |
| void split (const std::string& text, const std::string& separators, |
| std::list<std::string, |
| std::allocator<std::string> >& words) { |
| |
| size_t n = text.length (); |
| size_t start = text.find_first_not_of (separators); |
| |
| while (start < n) { |
| size_t stop = text.find_first_of (separators, start); |
| if (stop > n) stop = n; |
| words.push_back (text.substr (start, stop-start)); |
| start = text.find_first_not_of (separators, stop+1); |
| } |
| } |
| </PRE></UL> |
| <P>The program begins by finding <SAMP>start</SAMP>, the index of the first character that is <I>not</I> a separator. The loop then looks for <SAMP>stop</SAMP>, the index of the next character that <I>is</I> a separator, or uses the end of the string if no such value is found. These two indexes delimit a word, which is copied out of the text using a substring operation and inserted into the <B><I><A HREF="../stdlibref/list.html">list</A></I></B> of words. A search is then made to discover the start of the next word, and the loop continues. When the index value exceeds the limits of the <B><I><A HREF="../stdlibref/basic-string.html">string</A></I></B>, execution stops.</P> |
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