需要代码帮助以从 C++ 文件中读取特定字符串值并打印该值

Question

我是 C++ 编程的新手，我需要编写代码来从文件中读取特定值。例如，如果输入服务器名，则它必须显示 ABCDE-1。我正在尝试使用字符串函数，但无法获得结果。有没有人帮忙写下逻辑。

文件数据

[ServerName]
ABCDE-1;
[DBLcation]
\ABCDE-1\dat-520;
[ServerAPPsharename]
LR520APP;
[DerTablePath]
\ABCDE-1\dat-520\CDM\derd;
[PTPWait]
9995;

第一部分是文件数据谢谢

读取字符串数组中的文件数据。

string str;
string Database[10];
if (myfile.is_open()) 
{
int i=0;
while (myfile)
{
getline(myfile, str);
// here I am trying to store each word in  array of string
//Database[i]=str; 
i++;
}
}
else
{
cout << "Error in opening file\n";
}

打印所选选项。

cout<<"Enter what you want "<<endl;
cout<<"1.-ServerName \n2.-DBLcation \n3.-ServerAPPsharename \n4.-DerTablePath \n5.-PTPWait"<<endl;

我需要编写代码来打印文件中所选选项的值。

Answer 1

我们可以看到您的源数据遵循特定模式。

括号[]中有一个“键”，后面是一个“值”，后面跟一个分号;

如果我们有这样一个清晰的模式，那么我们就可以使用简单的机制。在“形式语言”理论中，根据乔姆斯基层次结构定义，我们称其为“Type-3 文法”或“正则文法”。请阅读 here。

优点是：您不需要解析器。在这种情况下，您可以使用所谓的正则表达式生存。

并且，C++ 支持带有 regex library 的正则表达式。

我将使用以下正则表达式来匹配上述模式：\[([^\]]+)\]\s+([^; ]+);

如果您将其粘贴到像 regex101 这样的正则表达式在线工具中，那么您就可以对其进行测试。描述是：

[([^]]+)]\s+([^; ]+);

\[([^\]]+)\]\s+([^; ]+);

\[ matches the character [ with index 9110 (5B16 or 1338) literally (case sensitive)
1st Capturing Group ([^\]]+)
Match a single character not present in the list below [^\]]
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
\] matches the character ] with index 9310 (5D16 or 1358) literally (case sensitive)
\] matches the character ] with index 9310 (5D16 or 1358) literally (case sensitive)
\s
matches any whitespace character (equivalent to [\r\n\t\f\v ])
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
2nd Capturing Group ([^; ]+)
Match a single character not present in the list below [^; ]
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
; 
matches a single character in the list ; (case sensitive)
; matches the character ; with index 5910 (3B16 or 738) literally (case sensitive)

下一个：

我们将使用std::map来存储数据。我们可以使用它的 map 运算符来存储和以访问键的值。

如果你想存储一个新值，那么你可以使用例如config["ServerAPPsharename"] = "LR520APP"。而且，如果你想通过键访问一个值，那么你可以写 std::cout << config["ServerAPPsharename"];

我们可以简单地遍历所有匹配项（只要有）并将数据存储在 std::map 中。我们将为此使用 regex_search。

然后我们可以轻松访问所有数据。

请将下面的代码作为许多可能的解决方案之一。

#include <iostream>
#include <fstream>
#include <string>
#include <regex>
#include <map>
#include <iomanip>

std::regex re{R"(\[([^\]]+)\]\s+([^; ]+);)"};

const std::string configFileName{ "test.txt" };

int main() {
    // Open the source file with config data and check, if it could be opened successfully
    if (std::ifstream configFileStream{ configFileName }; configFileStream) {

        // Load the complete content of the file in this string
        std::string configData(std::istreambuf_iterator<char>(configFileStream), {});

        // We will use an associative container to store the key and its value. 
        std::map<std::string, std::string> config{};

        // Now iterate over all pattern matches and store the data in our map
        for (std::smatch sm; std::regex_search(configData, sm, re); configData = sm.suffix())
            config[sm[1]] = sm[2];

        // Example: show value for ServerAPPsharename
        std::cout << "ServerAPPsharename: " << config["ServerAPPsharename"] << "\n\n";

        // show all config data
        std::cout << "\nAll data:\n\n";
        for (const auto& [key, value] : config) std::cout << std::setw(20) << key << ":  " << value << '\n';
    }
    else { // Error, could not open source file. Show message
        std::cerr << "\nError: Could not open '" << configFileName << "'\n\n";
    }
    return 0;
}

Answer 2

#include "stdafx.h"
#include<iostream>
#include<fstream>
#include<string>
using namespace std;
 
void read_file();


int main()
{
    read_file();
    return 0;
}
void read_file()
{
    ifstream myfile;
    myfile.open("config.txt");
    string str;
    if (myfile.is_open())
    {
        cout << "Enter the name :" << endl;
        string in_val;
        cin >> in_val;
        while (getline(myfile, str))
        {           
            if (str == "[" + in_val + "]")
            {
                getline(myfile, str);
                cout << str << endl;
            }
            
        }
     }
    else
        cout << "Error in opening file\n";
}

需要代码帮助以从 C++ 文件中读取特定字符串值并打印该值

Need help in code to read a particular string value from a file in C++ and print that value

c++

visual-c++

c++11