在C ++中将结构数据类型传递给命名管道

Question

I found one sample program that passes string from client to server in named pipes. How can I pass a struct data type through named pipes in c++?

WriteFile function of client looks like this:

WriteFile(hPipe,TEXT("Hello Pipe\n"),12,&dwWritten,NULL);

ReadFile function of server looks like this:

while (ReadFile(hPipe, buffer, sizeof(buffer)-1, &dwRead, NULL))

The structure I need to pass looks like this:

struct EventLogEntry 
   {
       string date;
       string time;
       string subsystem;
       unsigned long eventType;
       string majorFunction;
       string messageText;
       unsigned long timeStamp; //Added for TimeZone Corrections
   };

In CreateNamedPipe() I'm using PIPE_TYPE_BYTE PIPE_READMODE_BYTE pipe mode. Do I need to change them to PIPE_TYPE_BYTE and PIPE_READMODE_MESSAGE ?

Answer 1

You cannot pass instances of a class across the wire.

You basically have two options.

A) Use fixed size buffers:

struct mydata {
  char message[200];
  char name[50];
  int time;
};

and just send sizeof(mydata) across the pipe.

B) Marshal the data in a different format:

struct mywiredata {
  int messageoffset;
  int nameoffset;
  int time;
  char buffer[ANYSIZE_ARRAY]; //blogs.msdn.microsoft.com/oldnewthing/20040826-00/?p=38043
};

Here you basically have a fixed header portion with all the strings stored as bytes at the end. You find the start of a string by accessing the buffer at the appropriate offset. You need marshalling code at each end of the pipe to convert to/from your EventLogEntry and mywiredata structs.