Simple Mailslot program not working?

Question

Using the client and server examples found here: http://www.winsocketdotnetworkprogramming.com/winsock2programming/winsock2advancedmailslot14.html Compiling them with VS2008, running the server and then "client Myslot" I keep getting "WriteFail failed with error 53." Anyone have any ideas? Links to other Mailslot examples are also welcome, thanks.

Server:

    // Server sample
#include <windows.h>
#include <stdio.h>

void main(void)
{

    HANDLE Mailslot;
    char buffer[256];
    DWORD NumberOfBytesRead;

    // Create the mailslot

    if ((Mailslot = CreateMailslot("\\\\.\\Mailslot\\Myslot", 0, MAILSLOT_WAIT_FOREVER, NULL)) == INVALID_HANDLE_VALUE)
    {
        printf("Failed to create a mailslot %d\n", GetLastError());
        return;
    } 

    // Read data from the mailslot forever!

    while(ReadFile(Mailslot, buffer, 256, &NumberOfBytesRead, NULL) != 0)
    {
        printf("%.*s\n", NumberOfBytesRead, buffer);
    }
}

Client:

// Client sample

#include <windows.h>
#include <stdio.h>

void main(int argc, char *argv[])
{
    HANDLE Mailslot;
    DWORD BytesWritten;
    CHAR ServerName[256];

    // Accept a command line argument for the server to send a message to

    if (argc < 2)
    {
        printf("Usage: client <server name>\n");
        return;
    }

    sprintf(ServerName, "\\\\%s\\Mailslot\\Myslot", argv[1]);

    if ((Mailslot = CreateFile(ServerName, GENERIC_WRITE,

        FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL)) == INVALID_HANDLE_VALUE)
    {
        printf("CreateFile failed with error %d\n", GetLastError());
        return;
    }

    if (WriteFile(Mailslot, "This is a test", 14, &BytesWritten, NULL) == 0)
    {
        printf("WriteFile failed with error %d\n", GetLastError());
        return;
    }

    printf("Wrote %d bytes\n", BytesWritten);
    CloseHandle(Mailslot);
}

Answer 1

Error 53 is ERROR_BAD_NETPATH, "The network path was not found". Clearly you are using the wrong server name for the mailslot. Use \\.\mailslot\blah if the server runs on the same machine as your client. And don't forget to escape the backslash in a string: "\\\\.\\mailslot\\blah".

Answer 2

I copied the code exactly as posted into two files, compiled them with VS2008 and they ran perfectly. If your client program is compiled as client.exe, then type the following command:

client .

or

client <computername>

where computer name is the PC's name without the domain. You can call the API GetComputerName to retrieve the name.