Boost學習筆記5-Boost-StringAlgorithms

喜歡這篇文章嗎？喜歡的話去看博主的置頂博客，即可依據分類找到此文章的原版得到更好的體驗，

圖片及代碼顯示的問題，筆者深感抱歉，想要更好的體驗去原博文即可。

---

title: Boost學習筆記5 - Boost::StringAlgorithms
mathjax: true
date: 2020-03-17 19:56:26
categories: [c++筆記,Boost學習筆記]
tags: [c++筆記,Boost學習筆記]
keywords: [c++筆記,Boost學習筆記]

---

StringAlgorithms

   我終於找到一個暫時沒有被編入C++17的庫了，聽說在C++20中他也沒進，哈哈哈。

大小寫轉化

   首先上來的肯定就是大小寫轉化啦，使用函數to_upper_copy(string)就可以了。

#include <boost/algorithm/string.hpp>
#include <iostream>

int main() {
  std::string s = "abcdefgABCDEFG";
  std::cout << boost::algorithm::to_upper_copy(s) << std::endl;
  std::cout << boost::algorithm::to_lower_copy(s) << std::endl;
}

刪除子串

   erase_all_copy就是說先copy一份，然後再將子串全部刪除，如果不帶copy就是說直接操作穿進去的母串。下面的代碼都可以去掉_copy,erase_first指的是刪除第一次出現的，last指的是刪除最後一次出現的，nth指的是刪除第n次出現的，n從0開始,erase_head值的是刪除前n個字符，erase_tail指的是刪除後n個字符。

#include <boost/algorithm/string.hpp>
#include <iostream>

int main() {
  std::string s = "000111000111ababab000111000111";
  std::cout << s << std::endl;

  // boost::algorithm::erase_all(s,"ab");
  std::cout << boost::algorithm::erase_all_copy(s, "ab") << std::endl;
  std::cout << boost::algorithm::erase_first_copy(s, "111") << std::endl;
  std::cout << boost::algorithm::erase_last_copy(s, "111") << std::endl;
  std::cout << boost::algorithm::erase_nth_copy(s, "111",0) << std::endl;
  std::cout << boost::algorithm::erase_nth_copy(s, "111",100) << std::endl;
  std::cout << boost::algorithm::erase_head_copy(s, 4) << std::endl;
  std::cout << boost::algorithm::erase_tail_copy(s, 4) << std::endl;
}

查找子串

   find一類的函數，同上,他將返回一個iterator_range的迭代器。這個迭代器可以操作子串。注意子串和母串共享空間。

#include <boost/algorithm/string.hpp>
#include <iostream>

int main() {
  std::string s = "000111000111ababab000111000111";
  std::cout << s << std::endl;
  auto x = boost::algorithm::find_first(s,"000");
  x[0] = '2';
  std::cout << s << std::endl;
  //std::cout << boost::algorithm::find_last(s, "111") << std::endl;
}

   又是一套代碼下來了

#include <boost/algorithm/string.hpp>
#include <iostream>

int main() {
  std::string s = "000111000111ababab000111000111";
  std::cout << s << std::endl;
  auto x = boost::algorithm::find_first(s,"000");
  x = boost::algorithm::find_last(s,"1");
  x = boost::algorithm::find_nth(s,"1",3);
  x = boost::algorithm::find_tail(s,3);
  x = boost::algorithm::find_head(s,3);
  std::cout << s << std::endl;
  //std::cout << boost::algorithm::find_last(s, "111") << std::endl;
}

替換子串

   replace又是一套如下

#include <boost/algorithm/string.hpp>
#include <iostream>

int main() {
  std::string s = "000111000111ababab000111000111";
  std::cout << s << std::endl;

  // boost::algorithm::replace_all(s,"ab");
  std::cout << boost::algorithm::replace_all_copy(s, "ab","all") << std::endl;
  std::cout << boost::algorithm::replace_first_copy(s, "111","first") << std::endl;
  std::cout << boost::algorithm::replace_last_copy(s, "111","last") << std::endl;
  std::cout << boost::algorithm::replace_nth_copy(s, "111", 0,"nth") << std::endl;
  std::cout << boost::algorithm::replace_nth_copy(s, "111", 100,"nth") << std::endl;
  std::cout << boost::algorithm::replace_head_copy(s, 2,"Head") << std::endl;
  std::cout << boost::algorithm::replace_tail_copy(s, 2,"Tail") << std::endl;
}

修剪字符串

   trim_left_copy 指的是從左邊開始修建，刪掉空字符等，trim_right_copy是從右邊開始修建，trim_copy是兩邊一起修剪。

#include <boost/algorithm/string.hpp>
#include <iostream>

int main() {
  std::string s = "\t  ab  d d  d d d \t";
  std::cout << "|" << s << "|" << std::endl;
  std::cout << "|" << boost::algorithm::trim_left_copy(s) << "|" << std::endl;
  std::cout << "|" << boost::algorithm::trim_right_copy(s) << "|" << std::endl;
  std::cout << "|" << boost::algorithm::trim_copy(s) << "|" << std::endl;
}

   這個代碼輸出了

|	  ab  d d  d d d 	|
|ab  d d  d d d 	|
|	  ab  d d  d d d|
|ab  d d  d d d|

   我們還可以通過指定謂詞來修剪使用trim_left_copy_if

#include <boost/algorithm/string.hpp>
#include <iostream>

int main() {
  std::string s = " 01 0 1 000ab  d d  d d d 11111111";
  std::cout << "|" << s << "|" << std::endl;
  std::cout << "|" << boost::algorithm::trim_left_copy_if(s,boost::algorithm::is_any_of(" 01")) << "|" << std::endl;
  std::cout << "|" << boost::algorithm::trim_right_copy_if(s,boost::algorithm::is_any_of(" 01")) << "|" << std::endl;
  std::cout << "|" << boost::algorithm::trim_copy_if(s,boost::algorithm::is_any_of(" 01")) << "|" << std::endl;
}

   更多的謂詞,我們還有is_lower、is_upper、is_space等謂詞。

#include <boost/algorithm/string.hpp>
#include <iostream>

int main() {
  std::string s = " 01 0 1 000ab  d d  d d d 11111111";
  std::cout << "|" << s << "|" << std::endl;
  std::cout << "|" << boost::algorithm::trim_copy_if(s,boost::algorithm::is_space()) << "|" << std::endl;
  std::cout << "|" << boost::algorithm::trim_copy_if(s,boost::algorithm::is_digit()) << "|" << std::endl<<std::endl;
  s = "aaaBBBaBBaaa";
  std::cout << "|" << s << "|" << std::endl;
  std::cout << "|" << boost::algorithm::trim_copy_if(s,boost::algorithm::is_lower()) << "|" << std::endl;


}

字符串比較

   starts_with(s,t)判斷s是否以t開頭，類似的有ends_with,contains,lexicographical_compare分別表示s是否以t結尾，s是否包含t，s與t的字典序比較。

#include <boost/algorithm/string.hpp>
#include <iostream>

int main() {
  std::cout << boost::algorithm::starts_with("abcde", "abc") << std::endl;
  std::cout << boost::algorithm::ends_with("abcde", "cde") << std::endl;
  std::cout << boost::algorithm::contains("abcde", "cde") << std::endl;
  std::cout << boost::algorithm::lexicographical_compare("abcde", "cde") << std::endl;
  std::cout << boost::algorithm::lexicographical_compare("abcde", "abcde") << std::endl;
  std::cout << boost::algorithm::lexicographical_compare("cde", "abcde") << std::endl;
}

字符串分割

   這個就簡單多了，直接split+謂詞函數就行了

#include <boost/algorithm/string.hpp>
#include <iostream>

int main() {
  std::string s = "abc abc abc * abc ( abc )";
  std::vector<std::string> v;
  boost::algorithm::split(v, s, boost::algorithm::is_any_of(" *()"));
  for (auto x : v) std::cout << x << ".";
  std::cout << std::endl;
}

輸出

abc.abc.abc...abc...abc...

我們注意看有些函數前面有個i，比如ierase_all, 這個說的是忽略大小寫。