(原創) 如何使用for_each() algorithm? (C/C++) (STL)
很怀念VB和C#的foreach语法吗?对于C++只能用for语法造成程序冗长觉得很烦吗?foreach的确对于container而言非常好用且精简,C++/CLI已经增加上了for each语法了,事实上,C++也可使用foreach喔,STL提供了for_each() algorithm,可以弥补这个缺憾。
for_each() algorithm会将每个iterator当作const iterator处理,若只用普通的function,直接将function name传入即可,别忘了function name本身也是个pointer,若要用template function,则必须将该template function转成function pointer才可传进for_each algorithm,以下范例demo for_each() algorithm的用法。
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/*
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(C) OOMusou 2006 http://oomusou.cnblogs.com
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Filename : GenericAlgo_for_each.cpp
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Compiler : Visual C++ 8.0
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Description : Demo how to use for_each algorithm.
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Applies a specified function object to each element
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in a forward order within a range and returns the
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function object.
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Release : 11/19/2006
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*/
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#include <iostream>
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#include <vector>
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#include <algorithm>
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template <class T>
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void coutIterator1(T &);
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void coutIterator2(int &);
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int main() {
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std::vector<int> ivec(3,1);
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void (*pf) (int &) = coutIterator1;
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for_each(ivec.begin(), ivec.end(), pf);
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std::cout << std::endl;
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for_each(ivec.begin(), ivec.end(), coutIterator2);
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return 0;
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}
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template <class T>
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void coutIterator1(T &iter) {
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std::cout << iter << std::endl;
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}
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void coutIterator2(int &i) {
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std::cout << i << std::endl;
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}
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for_each() algorithm不能修改iterator,若要修改iterator,需用transform() algorithm。
See Also
(原創) 如何正確的使用迴圈(使用for_each)? (C/C++) (STL) (template)
Reference
C++ Primer 3rd中文版 P.1145