C++ Builder 将 TMemoryStream 缓冲区读取为无效指针

Question

我正在尝试将 TMemoryStream 缓冲区的内容复制到 void 指针，下面您可以看到不起作用的示例代码 - void 缓冲区为空，但文本框包含有效大小 - 我用 winrar 大小检查了它。以下代码创建 exe 文件，但它的大小为 0.

void __fastcall TForm1::Button1Click(TObject *Sender)
{
    TMemoryStream* ms = new TMemoryStream();
    Download->Get("http://rarlab.com/rar/wrar521pl.exe",ms);
    this->Edit1->Text = ms->Size;
    void* buffer = malloc(ms->Size );
    ms->Read(buffer,ms->Size);
    FILE* pFile = fopen("test.exe","wb");
    fwrite(buffer,4,ms->Size,pFile);
    fclose(pFile);
    delete ms;
}

此外，我知道我可以轻松地将 TMemoryStream 缓冲区的内容保存到文件中，但我需要它的内容作为 void 指针，所以我写了下面的代码来测试它。

Answer 1

您从流中读取的代码几乎是正确的。您没有在读取之前将流的 Position 属性重置为 0，因此您实际上是从流的末尾读取，那里没有数据可读。

试试这个：

void __fastcall TForm1::Button1Click(TObject *Sender)
{
    TMemoryStream* ms = new TMemoryStream();
    try
    {
        Download->Get("http://rarlab.com/rar/wrar521pl.exe", ms);
        ms->Position = 0; // <-- ADD THIS
        Edit1->Text = ms->Size;
        void* buffer = malloc(ms->Size);
        if (buffer)
        {
            ms->ReadBuffer(buffer, ms->Size);
            // ms->SaveToFile("test.exe");
            FILE* pFile = fopen("test.exe", "wb");
            if (pFile)
            {
                fwrite(buffer, 1, ms->Size, pFile);
                fclose(pFile);
            }
            free(buffer);
        }
    }
    __finally
    {
        delete ms;
    }
}

或者，根本不分配单独的缓冲区，而是直接使用流自己的缓冲区：

void __fastcall TForm1::Button1Click(TObject *Sender)
{
    TMemoryStream* ms = new TMemoryStream();
    try
    {
        Download->Get("http://rarlab.com/rar/wrar521pl.exe", ms);
        Edit1->Text = ms->Size;
        void* buffer = ms->Memory;
        // ms->SaveToFile("test.exe");
        FILE* pFile = fopen("test.exe", "wb");
        if (pFile)
        {
            fwrite(buffer, 1, ms->Size, pFile);
            fclose(pFile);
        }
    }
    __finally
    {
        delete ms;
    }
}

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