“访问冲突”，“分配错误”：POCO NTP客户端请求C ++

Question

I wanted to make a simple program which does the following: 'Get Atomic Time from Internet Clock'. I already did another program that uses FTP, and I did this with the Poco::Net library.

I tried using NTPClient, since I read that is the Network Time Protocol. In more detail, here is the information I worked with:

'The NIST servers listen for a NTP request on port 123, and respond by sending a udp/ip data packet in the NTP format. The data packet includes a 64-bit timestamp containing the time in UTC seconds since January 1, 1900 with a resolution of 200 ps.'

My source is this website: nist

Also, I tried various servers from here, which had the status 'all services available': servers

Here is a small example which crashes and/or throws an exception. It is an exception std::bad_alloc and sometimes it crashes with 'access violation' (see below). I am compiling with VC++12 on Windows 8

The docs I worked with: NTPClient

#include <iostream>
#include <stdexcept>

#include <Poco/Net/NTPClient.h>

using namespace Poco::Net;

int main()
{
    try {
        NTPClient client { IPAddress::Family::IPv4 };

             // this is where the bad_alloc comes from:
        client.request("129.6.15.30:123");  // or any other server

    }
    catch (std::exception& e) {
        std::cerr << e.message() << '\n';
    }
}

I don't know why this code is causing the bad_alloc Exception or access violation, so I hope someone can point out what I am doing wrong. I doubt it is a bug in the Library, I am probally just using it wrong (maybe it is?).

Update I also sometimes get '...0xC0000005: Access violation reading location 0x00E22CA9.' (the second memory location varies). However, depending on the IP-Address, the bad_alloc error still is caught sometimes (no crash). So for some IPs it crashes with access violation, with some it throws bad_alloc exception and terminates. Don't know if that piece of information might be helpful. Also, they error occurs, even if I feed complete garbage as IP-Address eg "foobar".

Until someone has an idea, I will examine the sources and try to find something (though that is hard with my level of experience).

Update2: After setting the libs to debug libs (I wanted more information, wanted to add the PocoNetd.pdb (I think it allows VS to debug pocos code too?) it doesn't happen anymore... weird, programming is weird...

Answer 1

I was not able to find a problem with POCO here. But there is a problem with posted code - there is no such thing as std::exception::message() so the code does not compile. Changing the message() to what() and executing, one gets "Host not found" exception description. Changing NTP server to "pool.ntp.org", it executes fine. Here's the code that runs well for me on Windows 8, VS2013, 64-bit build:

#include <iostream>
#include <stdexcept>
#include <Poco/Net/NTPClient.h>
using namespace Poco::Net;

int main()
{
    try {
        NTPClient client{ IPAddress::Family::IPv4 };
        client.request("pool.ntp.org");
    }
    catch (std::exception& e) {
        std::cerr << e.what() << '\n';
    }
}

EDIT: the reason for "Host not found" exception in the original code is because the port is embedded in the string passed to the request() call but the implementation hard codes the port and expects ip address or host name only.

EDIT2: Just an advice: If your goal is to run debug binaries, then you may consider your problem solved. Otherwise, you should be able to build and run a release build of your application with release versions of POCO libraries. For an example how to do that, look into any of the Poco::Net sample VS projects settings.

Answer 2

After setting the libs to debug libs (I wanted more information, wanted to add the PocoNetd.pdb (I think it allows VS to debug pocos code too?) it doesn't happen anymore... weird, programming is weird... I am also able so successfully compile and run a realease version.

So in a nutshell: I messed up my settings, and POCO yet has worked flawlessly for me. It's interesting, what kind of errors you get by messing up Debug/Release.