C++ mismatch(STL mismatch)算法详解
mismatch() 的 4 个版本和 equal() 一样有相同的参数——第二个序列有或没有结束迭代器,有或没有定义比较的额外的函数对象参数。mismatch() 返回的 pair 对象包含两个迭代器。它的 first 成员是一个来自前两个参数所指定序列的迭代器,second 是来自于第二个序列的迭代器。当序列不匹配时,pair 包含的迭代器指向第一对不匹配的元素;因此这个 pair 对象为 pair<iter1+n,iter2 + n>,这两个序列中索引为 n 的元素是第一个不匹配的元素。
当序列匹配时,pair 的成员取决于使用的 mismatch() 的版本和具体情况。iter1 和 end_iter1 表示定义第一个序列的迭代器,iter2 和 end_iter2 表示第二个序列的开始和结束迭代器。返回的匹配序列的 pair 的内容如下:
对于 mismatch(iter1,end_iter1,iter2):
- 返回 pair<end_iter1,(iter2 + (end_ter1 - iter1))>,pair 的成员 second 等于 iter2 加上第一个序列的长度。如果第二个序列比第一个序列短,结果是未定义的。
对于 mismatch(iterl, end_iter1, iter2, end_iter2):
- 当第一个序列比第二个序列长时,返回 pair<end_iter1, (iter2 + (end_iter1 - iter1))>,所以成员 second 为 iter2 加上第一个序列的长度。
- 当第二个序列比第一个序列长时,返回 pair<(iter1 + (end_iter2 - iter2)),end_iter2>, 所以成员 first 等于 iter1 加上第二个序列的长度。
- 当序列的长度相等时,返回 pair<end_iter1, end_iter2>。
不管是否添加一个用于比较的函数对象作为参数,上面的情况都同样适用。
下面是一个使用带有默认相等比较的 mismatch() 的示例:
// Using the mismatch() algorithm #include <iostream> // For standard streams #include <vector> // For vector container #include <algorithm> // For equal() algorithm #include <string> // For string class #include <iterator> // For stream iterators using std::string; using word_iter = std::vector<string>::iterator; int main() { std::vector<string> words1 {"one", "two", "three", "four", "five", "six", "seven", "eight", "nine"}; std::vector<string> words2 {"two", "three", "four", "five", "six", "eleven", "eight", "nine", "ten"}; auto iter1 = std::begin(words1); auto end_iter1 = std::end(words1); auto iter2 = std::begin(words2); auto end_iter2 = std::end(words2); // Lambda expression to output mismatch() result auto print_match = [](const std::pair<word_iter, word_iter>& pr, const word_iter& end_iter) { if(pr.first != end_iter) std::cout << "\nFirst pair of words that differ are "<< *pr.first << " and " << *pr.second << std::endl; else std::cout << "\nRanges are identical." << std::endl; }; std::cout << "Container - words1: "; std::copy(iter1, end_iter1, std::ostream_iterator<string>{std::cout, " "}); std::cout << "\nContainer - words2: "; std::copy(iter2, end_iter2, std::ostream_iterator<string>{std::cout, " "}); std::cout << std::endl; std::cout << "\nCompare from words1[1] to end with words2:"; print_match(std::mismatch(iter1 + 1, end_iter1, iter2), end_iter1); std::cout << "\nCompare from words2[0] to second-to-last with words1:"; print_match(std::mismatch(iter2, end_iter2 - 1, iter1), end_iter2 - 1); std::cout << "\nCompare from words1[1] to words1[5] with words2:"; print_match(std::mismatch(iter1 + 1, iter1 + 6, iter2), iter1 + 6); std::cout << "\nCompare first 6 from words1 with first 6 in words2:"; print_match(std::mismatch(iter1, iter1 + 6, iter2, iter2 + 6), iter1 + 6); std::cout << "\nCompare all words1 with words2:"; print_match(std::mismatch(iter1, end_iter1, iter2), end_iter1); std::cout << "\nCompare all of words2 with all of words1:"; print_match(std::mismatch(iter2, end_iter2, iter1, end_iter1), end_iter2); std::cout << "\nCompare from words1[1] to end with words2[0] to second-to-last:"; print_match(std::mismatch(iter1 + 1, end_iter1, iter2, end_iter2 - 1), end_iter1); }注意 words2 中的内容和前面示例中的有些不同。每一次应用 mismatch() 的结果都是由定义为 print_match 的 lambda 表达式生成的。它的参数是一个 pair 对象和一个 vector<string> 容器的迭代器。使用 using 指令生成 word_iter 别名可以使 lambda 表达式的定义更简单。
在 main() 的代码中使用了不同版本的 mismatch(),它们都没有包含比较函数对象的参数。如果第二个序列只用开始迭代器指定,为了和第一个序列匹配,它只需要有和第一个序列相等长度的元素,但也可以更长。如果第二个序列是完全指定的,会由最短的序列来确定比较多少个元素。
输出如下:
Container - words1: one two three four five six seven eight nine
Container - words2: two three four five six eleven eight nine ten
Compare from words1[1] to end with words2:
First pair of words that differ are seven and eleven
Compare from words2[0] to second-to-last with words1:
First pair of words that differ are two and one
Compare from words1[1] to words1[5] with words2:
Ranges are identical.
Compare first 6 from words1 with first 6 in words2:
First pair of words that differ are one and two
Compare all words1 with words2:
First pair of words that differ are one and two
Compare all of words2 with all of words1:
First pair of words that differ are two and one
Compare from words1[1] to end with words2[0] to second-to-last:
First pair of words that differ are seven and eleven
std::vector<string> range1 {"one", "three", "five", "ten"}; std::vector<string> range2 {"nine", "five", "eighteen”,"seven"}; auto pr = std::mismatch( std::begin(range1), std::end(range1),std:rbegin(range2), std::end(range2),[](const string& s1, const string& s2) { return s1.back() = s2.back(); }); if(pr.first == std::end(range1) || pr.second == std::end(range2)) std::cout << "The ranges are identical." << std::endl; else std::cout << *pr.first << " is not equal to " << *pr.second <<std::endl;当两个字符串的最后一个字符相等时,这个比较会返回 true,所以这段代码的输出为:
five is not equal to eighteen
当然,这是正确的,而且根据比较函数,“one”等于“nine”,“three”等于“five”。所有教程
- socket
- Python基础教程
- C#教程
- MySQL函数
- MySQL
- C语言入门
- C语言专题
- C语言编译器
- C语言编程实例
- GCC编译器
- 数据结构
- C语言项目案例
- C++教程
- OpenCV
- Qt教程
- Unity 3D教程
- UE4
- STL
- Redis
- Android教程
- JavaScript
- PHP
- Mybatis
- Spring Cloud
- Maven
- vi命令
- Spring Boot
- Spring MVC
- Hibernate
- Linux
- Linux命令
- Shell脚本
- Java教程
- 设计模式
- Spring
- Servlet
- Struts2
- Java Swing
- JSP教程
- CSS教程
- TensorFlow
- 区块链
- Go语言教程
- Docker
- 编程笔记
- 资源下载
- 关于我们
- 汇编语言
- 大数据
- 云计算
- VIP视频