Re: [Boost-users] Why is asio clobbering my file before it can be sent?

Subject: Re: [Boost-users] Why is asio clobbering my file before it can be sent?
From: TONGARI (tongari95_at_[hidden])
Date: 2011-08-18 04:01:09

2011/8/18 Andrew Yancy <andrew732_at_[hidden]>

> I've used the same boilerplate boost::asio code for years to send a plain
> text file "foo.txt" from a server back to a client and it has always worked
> fine.  Suddenly for no apparent reason, the same code I've always used with
> no problems now deletes the contents of foo.txt before it can actually be
> sent to the client.  I'm creating foo.txt with a different program now, but
> I don't see how that could make any difference on Win32.
>
> Below is the relevant part of the code just before I use boost::asio::write
> to send the contents of foo.txt back to the client.  As shown by the two
> printf statements, the contents of the file are somehow lost when the file
> name and size are sent to the client.  Anyone know what's going on?  Is
> there any other information I can provide to shed light on the problem?
>  Thanks very much for any help~
>
>
>
>
> std::ifstream source_file("foo.txt", std::ios_base::binary |
> std::ios_base::ate);
> if (!source_file)
>   return __LINE__;
> size_t file_size = source_file.tellg();
> source_file.seekg(0);
>
> printf("foo.txt size: %d\n", (int) file_size); //size is OK here
>
> boost::asio::streambuf request;
> std::ostream request_stream(&request);
> request_stream << return_fn << "\n" << file_size << "\n\n";
> boost::asio::write(socket, request);
>
> file_size = source_file.tellg();
> printf("foo.txt size: %d\n", (int) file_size); //size is now 0!
>

I see no relation between asio and your source_file.
I only see that you called "file_size = source_file.tellg()" after
"source_file.seekg(0)".