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我正在编写一个程序来将文件从一台 PC 发送到另一台 PC。我正在尝试使用 发送它char* buffer，但我遇到了一些问题。我认为它发送缓冲区，但结果是一个大小为 0 KB 的文件。我怀疑我没有将缓冲区写入文件，但我真的不确定。我的缓冲区数据来自 *bmp 文件。我确实在几乎同一件事上找到了另一个问题，但我真的需要更多解释。

我正在使用 C++ Builder 2010，很难找到任何教程。它具有可能有用的各种组件和功能。

编码：

客户端：

void __fastcall TForm1::TcpServer1Accept(TObject *Sender,
    TCustomIpClient *ClientSocket)
{
  char *buffer;
  TcpServer1->ReceiveBuf(buffer, sizeof(buffer), 0);

  CreateFile(buffer); //function that creates a file from the buffer

  //Drawing my bmp on the form
  Slide->LoadFromFile("ScreenShotBorland.bmp");
  Image1->Canvas->Draw(0, 0, Slide);

  free(buffer);
}

void CreateFile(char *buffer)
{

  FILE *fp = NULL;

  fp = fopen("teste.bmp", "wb");
  if (fp == NULL) {
    MessageBox(NULL, "ERRO!", "Error", MB_OK | MB_ICONERROR);
  }

  fwrite(buffer, 1, sizeof(buffer), fp);
  free(buffer);
  fclose(fp);
}

服务器： 

void __fastcall TForm1::TcpClient1Connect(TObject *Sender)
{
  //Open a file to load the buffer
  long lSize;
  char *buffer;
  size_t result;
  FILE *pf2 = fopen("teste.bmp", "rb");

  if (pf2 == NULL) {
    MessageBox(NULL, "ERRO!", "Error", MB_OK | MB_ICONERROR);
  }

  fseek(pf2, 0, SEEK_END);
  lSize = ftell(pf2);
  rewind(pf2);

  //allocate the buffer in memorie
  buffer = (char*) malloc(sizeof(char) * lSize);
  if (buffer == NULL)
    MessageBox(NULL, "ERRO!", "Error", MB_OK | MB_ICONERROR);

  result = fread(buffer, 1, lSize, pf2);

  if (result != lSize)
    MessageBox(NULL, "ERRO!!!", "Error", MB_OK | MB_ICONERROR);

  //Transferring the file
  if (TcpClient1->Active)
    TcpClient1->SendBuf(buffer, sizeof(buffer), 0);

  free(buffer);
  fclose(pf2);
}
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1 回答 1

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  • Your client uses a TTcpServer, and your server uses a TTcpClient. This is confusing and possibly incorrect (either incorrect terminology or incorrect code).
  • For the BufSize parameter to SendBuf and ReceiveBuf, your code sends sizeof(buffer). buffer is a char * (pointer to char), and the size of a pointer is 32 bits on x86. sizeof tells the size of the variable itself, not what the variable points to. C and C++ don't even know the size of what the variable points to, because buffer could be uninitialized, or NULL, or it could just be an alias to another buffer elsewhere, and so on.
  • The "client" code (the one receiving the buffer) has no way of doing the size of data to expect. To fix this, you should probably send the size before sending the contents. Note that your CreateFile function will then need to take that size as a parameter so it knows how big buffer is.
  • The "client" code (the one receiving the buffer) never allocates space for the buffer.
  • Suggestion: CreateFile is a Windows API function. Your code would be easier to read if you avoid giving application-specific functions the same names as generic Windows API functions. CreateScreenshotFile or SaveScreenshot would probably be better.
于 2009-11-09T16:49:50.800 回答