Question

我需要将文件内容读入某些对象，遗憾的是我不能自由地使用std :: string，因此必须使用char指针。然而，当我这样做时，我会得到直接来自内存的奇怪迹象，solution然后就不起作用了。所以我通过直接从istream而不是std库使用getline来重建，但同样的事情发生了。如何在不使用std :: string的情况下正确读取文件。

PortsContainer game::ParsePort(std::istream& stream)
{
    PortsContainer ports;

    bool passFirstRow = false;

    char* portLine = new char[1000000];
    int i = 0;
    while (!stream.eof())
    {
        if (!stream)
            throw std::system_error(Error::STREAM_ERROR);

        if (portLine[0] == '\0' || portLine == nullptr || portLine[0] == '#')
            continue;

        std::stringstream ss(portLine);

        if (!passFirstRow) {
            char* name = new char[100];
            while (!ss.eof()) {
                ss.getline(name, sizeof name, ';');
                Port* port = new Port();
                //port->name = const_cast<char*>(name);
                port->name = const_cast<char*>(name);
                ports.addItem(port);
            }

            passFirstRow = true;
        } else {
            i++;
        }

        if (!stream)
            throw std::system_error(Error::STREAM_ERROR);
    }

    return ports;
}

PortsContainer game::ParsePort(std::istream& stream, std::error_code& errorBuffer)
{
    try
    {
        return ParsePort(stream);
    }
    catch (std::system_error exception)
    {
        errorBuffer = exception.code();
    }
}

PortsContainer game::GetAvailablePorts()
{
    PortsContainer ports;

    std::ifstream stream("./ports.csv");

    std::error_code errorBuffer;
    ports = ParsePort(stream, errorBuffer);
    if (errorBuffer)
        return PortsContainer();

    return ports;
}

Answer 1

您没有使用任何数据填充Button。实际上，您根本没有从portLine读取任何数据。

您滥用stream。直到首先尝试读取操作之后才会更新eof()标志。因此，您必须在仔细阅读eofbit之前阅读。

您正在泄漏eof()和portLine个缓冲区。更糟糕的是，由于您不允许使用name，这意味着std::string成员是Port::name指针，这意味着您（可能）有多个char*对象指向在内存中的相同物理缓冲区。如果Port稍后尝试释放该缓冲区，例如在其析构函数中，则会出现内存错误。

尝试更像这样的东西：

Port

但是，我强烈建议您使用STL智能指针来帮助确保更安全的内存管理：

PortsContainer game::ParsePort(std::istream& stream)
{
    if (!stream)
        throw std::system_error(Error::STREAM_ERROR);

    PortsContainer ports;

    bool passFirstRow = false;

    // better would be to use std::unique_ptr<char[]>, std::vector<char>,
    // or std::string instead so the memory is freed automatically ...
    char *portLine = new char[1000000];

    int i = 0;

    do
    {
        if (!stream.getline(portLine, 1000000))
        {
            delete[] portLine; // <-- free the buffer for line data...
            throw std::system_error(Error::STREAM_ERROR);
        }

        if ((stream.gcount() == 0) || (portLine[0] == '#'))
            continue;

        if (!passFirstRow)
        {
            std::istringstream iss(portLine);

            // better would be to use std::unique_ptr<char[]>, std::vector<char>,
            // or std::string instead so the memory is freed automatically ...
            char* name = new char[100];

            while (iss.getline(name, 100, ';'))
            {
                if (iss.gcount() == 0) continue;

                Port *port = new Port();
                port->name = name; // <-- assumes ownership is transferred!
                ports.addItem(port);
                name = new char[100]; // <-- have to reallocate a new buffer each time!
            }
            delete[] name; // <-- free the last buffer not used...
            passFirstRow = true;
        } else {
            ++i;
        }
    }
    while (!stream.eof());

    delete[] portLine; // <-- free the buffer for line data...

    return ports;
}

PortsContainer game::ParsePort(std::istream& stream, std::error_code& errorBuffer)
{
    try
    {
        return ParsePort(stream);
    }
    catch (const std::system_error &exception)
    {
        errorBuffer = exception.code();
        return PortsContainer(); // <-- don't forget to return something!
    }
}

PortsContainer game::GetAvailablePorts()
{
    std::ifstream stream("./ports.csv");
    std::error_code errorBuffer;
    return ParsePort(stream, errorBuffer); // <-- no need to check errorBuffer before returning!
}

尽管如此，使用PortsContainer game::ParsePort(std::istream& stream) { if (!stream) throw std::system_error(Error::STREAM_ERROR); PortsContainer ports; bool passFirstRow = false; // since you are using std::error_code, that means you are // using C++11 or later, so use std::unique_ptr to ensure // safe memory management... std::unique_ptr<char[]> portLine(new char[1000000]); int i = 0; do { if (!stream.getline(portLine.get(), 1000000)) throw std::system_error(Error::STREAM_ERROR); if ((stream.gcount() == 0) || (portLine[0] == '#')) continue; if (!passFirstRow) { std::istringstream iss(portLine.get()); // use std::unique_ptr here, too... std::unique_ptr<char[]> name(new char[100]); while (iss.getline(name.get(), 100, ';')) { if (iss.gcount() == 0) continue; // use std::unique_ptr here, too... std::unique_ptr<Port> port(new Port); port->name = name.release(); // <-- assumes ownership is transferred! // better to make Port::name use std::unique_ptr<char[]> and then std::move() ownership of name to it... ports.addItem(port.get()); port.release(); name.reset(new char[100]); // <-- have to reallocate a new buffer each time! } passFirstRow = true; } else { ++i; } } while (!stream.eof()); return ports; }将是最佳选择：

std::string

在c ++中只读取一个只有char指针的文件

1 个答案: