user199421 - Developer IT

Can't ping host from vmware guest using bridged networking

- by user199421

Host is Windows 7 Guest is Ubuntu 11.04 Network adapter is wireless I can ping other computers on the network but not the host. No firewall are involved. Sniffing the traffic with wireshark it looks like both the host and the guest are using the same MAC address. My guest simply doesn't receive a reply when asking for 192.168.1.101 (the host) My router has no problem giving both of them different IP addresses but maybe duplicate MAC address is the problem? It seems logical that both will have the same MAC address (from the host point of view) but it strange that there is no work around for this because otherwise I don't see how the host and guess are supposed to communicate.

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Will this SPF record restrict delivery of email for the original domain?

- by user199421

As part of the product we offer we send emails on behalf of our clients. Because the emails don't come from an IP associated with the client they are sometimes flagged as spam. We advised some of our clients to add an SPF record approving us to send emails on their behalf. We saw immediate improvement in deliverability rates after making the change however one of our clients was notified by his hosting provider that the SPF record we suggested to add would "slightly restrict" all emails that don't come from our servers (including our client's own servers). The record we use is this: v=spf1 a mx include:ourdomain.com ~all So my question is if the warning we received about this is correct and if so why and what can be done to solve this (allow sending email both from original domain and by ourselves).

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Returning c_str from a function

- by user199421

This is from a small library that I found online: const char* GetHandStateBrief(const PostFlopState* state) { static std::ostringstream out; ... rest of the function ... return out.str().c_str() Now in my code I am doing this: const char *d = GetHandStateBrief(&post); std::cout<< d << std::endl; Now, at first d contained garbage. I then realized that the c string I am getting from the function is destroyed when the function returns because std::ostringstream is allocated on the stack. So I added: return strdup( out.str().c_str()); And now I can get the text I need from the function. I have two questions: 1) Am I understanding this correctly? 2) I later noticed that the ostringstream was was allocated with static storage. Doesn't that mean that the object is supposed to stay in memory until the program terminates? and if so , then why can't I access the string?

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C++ extern keyword on functions. Why no just include the header file?

- by user199421

If I understand it correctly this means extern void foo(); that the function foo is declared in another translation unit. 1) Why not just #include the header in which this function is declared? 2) How does the linker know where to look for function at linking time?

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Why are forward declarations necessary?

- by user199421

In languages like C# and Java there is no need to declare (for example) a class before using it. If I understand it correctly this is because the compiler does two passes on the code. In the first it just "collects the information available" and in the second one it checks that the code is correct. In C and C++ the compiler does only one pass so everything needs to be available at that time. So my question basically is why isn't it done this way in C and C++. Wouldn't it eliminate the needs for header files?

Developer IT