在C ++中拆分字符串的最佳实践 [英] Best Practice to split a string in C++

问题描述

我正在学习竞争性编程的C ++.最近，我遇到了一个问题，需要将字符串拆分为向量(我来自Python和JavaScript背景，因此有一个简单的内置函数负责拆分字符串)

I am learning C++ for Competitive Programming. I recently came across a problem that requires a string to be split into a vector (I come from a Python and JavaScript background, so there's this easy built-in function that is responsible for splitting strings)

在C ++中是否有类似的东西?一种节省时间的简单方法.多谢您的投入

Is there something similar in C++? An easy way that saves time. I would appreciate your input

谢谢！

推荐答案

难以回答.由于竞争性编程与C ++的真正意图没有太大关系.

Difficult to answer. Since competetive programming has not so much to do with real intention of C++.

反正.

将字符串拆分为标记是一项非常古老的任务.有许多可用的解决方案.全部具有不同的属性.有些很难理解，有些很难开发，有些更复杂，更慢或更快，或者更灵活.

Splitting a string into tokens is a very old task. There are many many solutions available. All have different properties. Some are difficult to understand, some are hard to develop, some are more complex, slower or faster or more flexible or not.

替代品

1. 使用指针或迭代器手工制作的许多变体，可能难以开发并且容易出错.
2. 使用旧式 std :: strtok 函数.也许不安全.也许不应该再使用
3. std :: getline .最常用的实现.但是实际上是一个误用"而不是那么灵活
4. 使用专门为此目的而开发的专用现代功能，该功能最灵活且最适合STL环境和算法环境.但是比较慢.

1. Handcrafted, many variants, using pointers or iterators, maybe hard to develop and error prone.
2. Using old style std::strtok function. Maybe unsafe. Maybe should not be used any longer
3. std::getline. Most used implementation. But actually a "misuse" and not so flexible
4. Using dedicated modern function, specifically developed for this purpose, most flexible and good fitting into the STL environment and algortithm landscape. But slower.

请在一个代码中查看4个示例.

Please see 4 examples in one piece of code.

#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <regex>
#include <algorithm>
#include <iterator>
#include <cstring>
#include <forward_list>
#include <deque>

using Container = std::vector<std::string>;
std::regex delimiter{ "," };


int main() {

    // Some function to print the contents of an STL container
    auto print = [](const auto& container) -> void { std::copy(container.begin(), container.end(),
        std::ostream_iterator<std::decay<decltype(*container.begin())>::type>(std::cout, " ")); std::cout << '\n'; };

    // Example 1:   Handcrafted -------------------------------------------------------------------------
    {
        // Our string that we want to split
        std::string stringToSplit{ "aaa,bbb,ccc,ddd" };
        Container c{};

        // Search for comma, then take the part and add to the result
        for (size_t i{ 0U }, startpos{ 0U }; i <= stringToSplit.size(); ++i) {

            // So, if there is a comma or the end of the string
            if ((stringToSplit[i] == ',') || (i == (stringToSplit.size()))) {

                // Copy substring
                c.push_back(stringToSplit.substr(startpos, i - startpos));
                startpos = i + 1;
            }
        }
        print(c);
    }

    // Example 2:   Using very old strtok function ----------------------------------------------------------
    {
        // Our string that we want to split
        std::string stringToSplit{ "aaa,bbb,ccc,ddd" };
        Container c{};

        // Split string into parts in a simple for loop
#pragma warning(suppress : 4996)
        for (char* token = std::strtok(const_cast<char*>(stringToSplit.data()), ","); token != nullptr; token = std::strtok(nullptr, ",")) {
            c.push_back(token);
        }

        print(c);
    }

    // Example 3:   Very often used std::getline with additional istringstream ------------------------------------------------
    {
        // Our string that we want to split
        std::string stringToSplit{ "aaa,bbb,ccc,ddd" };
        Container c{};

        // Put string in an std::istringstream
        std::istringstream iss{ stringToSplit };

        // Extract string parts in simple for loop
        for (std::string part{}; std::getline(iss, part, ','); c.push_back(part))
            ;

        print(c);
    }

    // Example 4:   Most flexible iterator solution  ------------------------------------------------

    {
        // Our string that we want to split
        std::string stringToSplit{ "aaa,bbb,ccc,ddd" };


        Container c(std::sregex_token_iterator(stringToSplit.begin(), stringToSplit.end(), delimiter, -1), {});
        //
        // Everything done already with range constructor. No additional code needed.
        //

        print(c);


        // Works also with other containers in the same way
        std::forward_list<std::string> c2(std::sregex_token_iterator(stringToSplit.begin(), stringToSplit.end(), delimiter, -1), {});

        print(c2);

        // And works with algorithms
        std::deque<std::string> c3{};
        std::copy(std::sregex_token_iterator(stringToSplit.begin(), stringToSplit.end(), delimiter, -1), {}, std::back_inserter(c3));

        print(c3);
    }
    return 0;
}

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