C++编程思想 第2卷 第6章 通用算法 概述 判定函数

有时只想复制定义好的某个序列中的一个子集到另一个序列中
这个子集只满足某个特殊条件的那些元素组成

//: C06:CopyInts2.cpp
// From "Thinking in C++, Volume 2", by Bruce Eckel & Chuck Allison.
// (c) 1995-2004 MindView, Inc. All Rights Reserved.
// See source code use permissions stated in the file 'License.txt',
// distributed with the code package available at www.MindView.net.
// Ignores ints that satisfy a predicate.
#include <algorithm>
#include <cstddef>
#include <iostream>
using namespace std;

// You supply this predicate
bool gt15(int x) { return 15 < x; }

int main() {
  int a[] = { 10, 20, 30 };
  const size_t SIZE = sizeof a / sizeof a[0];
  int b[SIZE];
  int* endb = remove_copy_if(a, a+SIZE, b, gt15);
  int* beginb = b;
  while(beginb != endb)
    cout << *beginb++ << endl; // Prints 10 only
  getchar();
} ///:~

输出
10
remove_copy_if()函数模板需要一些通常用来限定范围的指针
还增加了一个用户自选的判定函数

copy算法的另外一个变种

//: C06:CopyStrings2.cpp
// From "Thinking in C++, Volume 2", by Bruce Eckel & Chuck Allison.
// (c) 1995-2004 MindView, Inc. All Rights Reserved.
// See source code use permissions stated in the file 'License.txt',
// distributed with the code package available at www.MindView.net.
// Replaces strings that satisfy a predicate.
#include <algorithm>
#include <cstddef>
#include <iostream>
#include <string>
using namespace std;

// The predicate
bool contains_e(const string& s) {
  return s.find('e') != string::npos;
}

int main() {
  string a[] = {"read", "my", "lips"};
  const size_t SIZE = sizeof a / sizeof a[0];
  string b[SIZE];
  string* endb = replace_copy_if(a, a + SIZE, b,
    contains_e, string("kiss"));
  string* beginb = b;
  while(beginb != endb)
    cout << *beginb++ << endl;
  getchar();
} ///:~

输出
kiss
my
lips

remove_copy_if()在输出一个序列时用一个固定的值来替代这些元素
replace_if()算法改变原始序列对应位置中的内容，而不是向单独的输出序列中
写数据

//: C06:ReplaceStrings.cpp
// From "Thinking in C++, Volume 2", by Bruce Eckel & Chuck Allison.
// (c) 1995-2004 MindView, Inc. All Rights Reserved.
// See source code use permissions stated in the file 'License.txt',
// distributed with the code package available at www.MindView.net.
// Replaces strings in-place.
#include <algorithm>
#include <cstddef>
#include <iostream>
#include <string>
using namespace std;

bool contains_e(const string& s) {
  return s.find('e') != string::npos;
}

int main() {
  string a[] = {"read", "my", "lips"};
  const size_t SIZE = sizeof a / sizeof a[0];
  replace_if(a, a + SIZE, contains_e, string("kiss"));
  string* p = a;
  while(p != a + SIZE)
    cout << *p++ << endl;
  getchar();
} ///:~

输出
kiss
my
lips