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<HTML><HEAD><TITLE>13.8 Miscellaneous Algorithms</TITLE></HEAD><BODY><A HREF="ug1.htm"><IMG SRC="images/banner.gif"></A><BR><A HREF="seq_4302.htm"><IMG SRC="images/prev.gif"></A><A HREF="booktoc1.htm"><IMG SRC="images/toc.gif"></A><A HREF="tindex1.htm"><IMG SRC="images/tindex.gif"></A><A HREF="ord_1635.htm"><IMG SRC="images/next.gif"></A><BR><STRONG>Click on the banner to return to the user guide home page.</STRONG><H2>13.8 Miscellaneous Algorithms</H2><P>In the final section we describe the remaining algorithms found in the standard library.</P><A NAME="13.8.1"><H3>13.8.1 Apply a Function to All Elements in a Collection</H3></A><A NAME="idx167"><!></A><P>The algorithm <SAMP>for_each()</SAMP> takes three arguments. The first two provide the iterators that describe the sequence to be evaluated. The third is a one-argument function. The <SAMP>for_each()</SAMP> algorithm applies the function to each value of the sequence, passing the value as an argument.</P><PRE>Function for_each (InputIterator first, InputIterator last, Function);</PRE><P>For example, the following code fragment, which uses the <SAMP>print_if_leap()</SAMP> function, will print a list of the leap years that occur between 1900 and 1997: </P><PRE> cout << "leap years between 1990 and 1997 are: "; for_each (1990, 1997, print_if_leap); cout << endl;</PRE><A HREF="sidebar1.htm#sidebar72"><IMG SRC="images/note.gif" BORDER=0> <STRONG>Results Produced by Side Effect</STRONG></A><P>The argument function is guaranteed to be invoked only once for each element in the sequence. The <SAMP>for_each()</SAMP> algorithm itself returns the value of the third argument, although this, too, is usually ignored.</P><P>The following example searches an array of integer values representing dates, to determine which vintage wine years were also leap years:</P><PRE> int vintageYears[] = {1947, 1955, 1960, 1967, 1994}; ... cout << "vintage years which were also leap years are: "; for_each (vintageYears, vintageYears + 5, print_if_leap); cout << endl;</PRE><P>Side effects need not be restricted to printing. Assume we have a function <SAMP>countCaps()</SAMP> that counts the occurrence of capital letters:</P><PRE>int capCount = 0;void countCaps(char c) { if (isupper(c)) capCount++; }</PRE><P>The following example counts the number of capital letters in a string value:</P><PRE> string advice = "Never Trust Anybody Over 30!"; for_each(advice.begin(), advice.end(),countCaps); cout << "upper-case letter count is " << capCount << endl;</PRE><BR><HR><A HREF="seq_4302.htm"><IMG SRC="images/prev.gif"></A> <A HREF="booktoc1.htm"><IMG SRC="images/toc.gif"></A><A HREF="tindex1.htm"><IMG SRC="images/tindex.gif"></A><A HREF="ord_1635.htm"><IMG SRC="images/next.gif"></A><P>©Copyright 1996, Rogue Wave Software, Inc.</P></BODY></HTML>⌨️ 快捷键说明
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