在 C++ 中读取只有字符指针的文件

Question

我需要将文件内容读入某些对象，不幸的是我不能随意使用 std::string，因此必须使用字符指针。但是，当我这样做时，我会直接从内存中得到奇怪的迹象，但是 solution 是行不通的。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] == '[=10=]' || 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 portLine。事实上，您根本没有从 stream 读取任何数据。

您在滥用 eof()。 eofbit 标志只有在第一次尝试读取操作之后才会更新。所以你必须先阅读 eof().

您正在泄漏 portLine 和 name 缓冲区。更糟糕的是，由于您不允许使用 std::string，这意味着 Port::name 成员是一个 char* 指针，这意味着您（可能）有多个 Port 对象指向在内存中的同一物理缓冲区。如果 Port 稍后尝试释放该缓冲区，例如在其析构函数中，您将遇到内存错误。

尝试更像这样的东西：

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!
}

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;

    // 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;
}

不过，使用 std::string 将是最佳选择：

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

    PortsContainer ports;

    bool passFirstRow = false;
    std::string portLine;
    int i = 0;

    while (std::getline(stream, portLine))
    {
        if (portLine.empty() || (portLine[0] == '#'))
            continue;

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

            while (std::getline(iss, name, ';'))
            {
                if (name.empty()) continue;

                std::unique_ptr<Port> port(new Port);
                port->name = name; // <-- make Port::name be std::string as well!
                ports.addItem(port.get());
                port.release();
            }
            passFirstRow = true;
        } else {
            ++i;
        }
    }

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

    return ports;
}

在 C++ 中读取只有字符指针的文件

Read a file with only char pointers in c++

c++

pointers

char

getline