使用C ++将字符串拆分为键/值对 [英] Split string into key-value pairs using C++

问题描述

我有一个像这样的字符串:

I have a string like this:

"CA: ABCD\nCB: ABFG\nCC: AFBV\nCD: 4567"

现在，": "从值中拆分键，而\n则将对分离.我想将键值对添加到C ++中的映射中.

Now ": " splits key from value while \n separates the pairs. I want to add the key-value pairs to a map in C++.

是否有考虑到优化的有效方法?

Is there any efficient way of doing this considering optimization in mind?

推荐答案

好，我在这里有两种方法.第一个是我一直使用的简单，显而易见的方法(性能很少成为问题).第二种方法可能更有效，但是我还没有进行任何正式的时间安排.

Well I have two methods here. The first one is the easy, obvious method that I use all the time (performance is rarely an issue). The second method is likely more efficient but I have not done any formal timings.

在我的测试中，第二种方法要快大约3倍.

In my tests the second method is about 3 times faster.

#include <map>
#include <string>
#include <sstream>
#include <iostream>

std::map<std::string, std::string> mappify1(std::string const& s)
{
    std::map<std::string, std::string> m;

    std::string key, val;
    std::istringstream iss(s);

    while(std::getline(std::getline(iss, key, ':') >> std::ws, val))
        m[key] = val;

    return m;
}

std::map<std::string, std::string> mappify2(std::string const& s)
{
    std::map<std::string, std::string> m;

    std::string::size_type key_pos = 0;
    std::string::size_type key_end;
    std::string::size_type val_pos;
    std::string::size_type val_end;

    while((key_end = s.find(':', key_pos)) != std::string::npos)
    {
        if((val_pos = s.find_first_not_of(": ", key_end)) == std::string::npos)
            break;

        val_end = s.find('\n', val_pos);
        m.emplace(s.substr(key_pos, key_end - key_pos), s.substr(val_pos, val_end - val_pos));

        key_pos = val_end;
        if(key_pos != std::string::npos)
            ++key_pos;
    }

    return m;
}

int main()
{
    std::string s = "CA: ABCD\nCB: ABFG\nCC: AFBV\nCD: 4567";

    std::cout << "mappify1: " << '\n';

    auto m = mappify1(s);
    for(auto const& p: m)
        std::cout << '{' << p.first << " => " << p.second << '}' << '\n';

    std::cout << "mappify2: " << '\n';

    m = mappify2(s);
    for(auto const& p: m)
        std::cout << '{' << p.first << " => " << p.second << '}' << '\n';
}

输出:

mappify1: 
{CA => ABCD}
{CB => ABFG}
{CC => AFBV}
{CD => 4567}
mappify2: 
{CA => ABCD}
{CB => ABFG}
{CC => AFBV}
{CD => 4567}

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