c++ string as c string

Hello..

Im working on mx dns resolver and I'm making a header that has to be sent to nameserver..
Normally I would make the header with c string that way (or copy the packed struct to char):
unsigned char dns[512] = {1,1, 1,0, 0,1, 0,0, 0,0, 0,0};

How should I do this with c++ string? What would be the proper way?

Thanks

Code:

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std::string dns = "111001000000";

dns.c_str(); // Returns a (const?) char* to the string in the object

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You want something like this, I suppose? If you're in a situation where you have to use a union and struct to send and receive this header without conversion errors, then you may be better off using an array. I'm not sure a string object directly reflects the size of the string it holds. I wouldn't quote me on that, though. It can be tricky introducing C++ into network libraries that are written for C.

If you know the size of the array, and are not going to be manipulating it directly, then what you have:

Code:

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unsigned char dns[512] = {1,1, 1,0, 0,1, 0,0, 0,0, 0,0};

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Is fine, no need to go after STL just to be a hit up every language feature. If you need to concatenate a bunch of stuff into some sort of container, you could do some funny stuff with a vector I guess:

Code:

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unsigned char dns[512] = {1, 1, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0}; // does it need to be 512?
unsigned char moredata[512] = { 0 }; // more data you need to build into something?
std::vector<unsigned char> v;

v.resize(sizeof dns);
std::copy(dns, dns + sizeof dns, v.begin());

v.resize(v.size() + sizeof moredata);
std::copy(moredata, moredata + sizeof moredata, v.begin() + sizeof dns);

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Or something.

Quote:

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Code:

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std::string dns = "111001000000";

dns.c_str(); // Returns a (const?) char* to the string in the object

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You want something like this, I suppose? If you're in a situation where you have to use a union and struct to send and receive this header without conversion errors, then you may be better off using an array. I'm not sure a string object directly reflects the size of the string it holds. I wouldn't quote me on that, though. It can be tricky introducing C++ into network libraries that are written for C.

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That string will contain ascii values, and stuff. His data is not null-terminated and not really meant to be represented by a string.

Lets say I have a packed structure header (struct dnsheader) filled with data..

Code:

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dnsheader *header = makeheader();
char *query = new char[512];

memset(query, 0, 512);
memcpy(query, header, sizeof(dnsheader));

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How should I copy struct to c++ string? What would be the proper way to do this?

Code:

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dnsheader *header = makeheader();

std::string query( (char *) header, sizeof(dnsheader) );

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Quote:

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Originally Posted by Cat

Code:

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dnsheader *header = makeheader();

std::string query( (char *) header, sizeof(dnsheader) );

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This wont work.. I get error..

What about something like:

string query += header;

that wouldnt be okay, but what would be?
Would it be better to use vector as Tonto said, since my data wont be null-terminated.. And It wont contain only header..

>This wont work.. I get error..
Post what error you're getting.