C++ 字符串流问题：getline 不适用于 stringstream

Question

我编写了一个程序，它获取一个文件并将其读入 class 中的字符串流字段，现在我正尝试与它进行交互。问题是，当从几种方法中顺序读取时，其中一种方法会出错，或者根本不起作用。我想问题是我如何读取文件，我应该如何改进它？

有我的class:

class MatReader
{
protected:
    ...
    stringstream text;
    ...
    string PhysicsMaterial;
    string Diffuse;
    string NMap;
    string Specular;

public:
    /// <summary>
    /// Read all lines in .mat document by string
    /// </summary>
    void ReadAllLines(string file_path);
    /// <summary>
    /// Getting PhysicsMaterial property
    /// </summary>
    string getPhysMaterial();
    /// <summary>
    /// Getting diffuse file path
    /// </summary>
    string getDiffuseLocation();
};

还有我的实现文件：

#include "MaterialHandler.h"

void MatReader::ReadAllLines(string mat_file)
{
    ifstream infile(mat_file);
    string str;
    if (infile.is_open())
    {
        ofile = true;
        while (!infile.eof())
        {
            getline(infile, str);
            text << str+"\n";
        }
    }
    else
        throw exception("[ERROR] file does not exist or corrupted");
}

string MatReader::getPhysMaterial()
{
    string line;
    vector<string> seglist;
    try
    {
        if (ofile == false)
            throw exception("file not open");
    
        while (getline(text, line, '"'))
        {
            if (!line.find("/>"))
                break;
            seglist.push_back(line);
        }
        for (uint16_t i{}; i < seglist.size(); i++)
        {
            if (seglist[i-1] == " PhysicsMaterial=")
            {
                PhysicsMaterial = seglist[i];
                return seglist[i];
            }
        }
        line.clear();
        seglist.clear();
    }
    catch (const std::exception& ex)
    {
        cout << "[ERROR]: " << ex.what() << endl;
        return "[ERROR]";
    }
}

string MatReader::getDiffuseLocation()
{
    string line;
    vector<string> seglist;
    try
    {
        if (ofile == false)
            throw exception("file not open");
        while (getline(text, line, '"'))
        {
            seglist.push_back(line);
        }
        for (uint16_t i{}; i < seglist.size(); i++)
        {
            if (seglist[i - 1] == " File=")
            {
                PhysicsMaterial = seglist[i];
                return seglist[i];
            }
        }
    }
    catch (const std::exception& ex)
    {
        cout << "[ERROR]: " << ex.what() << endl;
        return "[ERROR]";
    }
}

方法“getPhysMaterial()”和“getDiffuseLocation()”单独运行没有任何问题，但如果按顺序执行，它们会报错或根本不执行。谢谢。

Answer 1

因此，首先您需要更正数组访问超出范围的问题。您遇到的下一个问题是您需要重置流的位置以便从头重新读取它。

这是一个如何做到这一点的例子。

std::stringstream ss{ };
ss << "This is line one\n"
   << "This is line two\n"
   << "This is line three\n"
   << "This is line four\n";

// Points to the start of the stringstream.
// You can store this as a member of your class.
const std::stringstream::pos_type start{ ss.tellg( ) };

std::string line{ };
while ( std::getline( ss, line ) )
    std::cout << line << '\n'; 

// Reset to the start of the stringstream.
ss.clear( );
ss.seekg( start );

while ( std::getline( ss, line ) )
    std::cout << line << '\n';

我注意到的另一个问题是您正在检查循环条件中的 eof。不要那样做.. Why is iostream::eof inside a loop condition (i.e. while (!stream.eof())) considered wrong?

改为执行以下操作：

std::stringstream ss{ };
if ( std::ifstream file{ "/Path/To/MyFile.txt" } )
{
    std::string input{ };
    while ( std::getline( file, input ) )
        ss << input << '\n';
}
else 
{
    std::cerr << "Failed to open file\n";
    return 1;
}

std::string line{ };
while ( std::getline( ss, line ) )
    std::cout << line << '\n';

C++ 字符串流问题：getline 不适用于 stringstream

C ++ string stream issue: getline doesn't work with stringstream

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