C++中读取弹出选择框（自选）读入一个txt文本

该C++程序展示如何打开一个文件选择对话框，让用户选择文本文件，然后读取并显示文件内容。它使用了`GetOpenFileNameA`函数来实现文件选择，`ifstream`来读取文件，并进行字符串处理。

#include <iostream>
#include <fstream>
#include <string>
#include <windows.h>
#include <commdlg.h>

using namespace std;

int main() {
    // 打开文件选择对话框
    OPENFILENAMEA ofn;
    char szFile[260] = { 0 };
    ZeroMemory(&ofn, sizeof(ofn));
    ofn.lStructSize = sizeof(ofn);
    ofn.lpstrFile = szFile;
    ofn.nMaxFile = sizeof(szFile);
    ofn.lpstrFilter = "Text Files (*.txt)\0*.txt\0All Files (*.*)\0*.*\0";
    ofn.nFilterIndex = 1;
    ofn.Flags = OFN_PATHMUSTEXIST | OFN_FILEMUSTEXIST | OFN_NOCHANGEDIR;

    if (GetOpenFileNameA(&ofn) == TRUE) {
        // 将 char 类型字符串转换为 wchar_t 类型字符串
        int len = MultiByteToWideChar(CP_UTF8, 0, szFile, -1, NULL, 0);
        wchar_t* wstr = new wchar_t[len];
        MultiByteToWideChar(CP_UTF8, 0, szFile, -1, wstr, len);
        wstring filename(wstr);
        delete[] wstr;

        ifstream infile(filename);

        if (!infile.is_open()) {
            cout << "Failed to open file." << endl;
            return 1;
        }

        string line;
        string text;
        while (getline(infile, line)) {
            text += line + "\n";
        }
        
        cout << "The content of the file is:\n" << text;

        infile.close();

        return 0;
    }
    else {
        cout << "User canceled the file selection dialog." << endl;
        return 1;
    }

}