Converting an std::string into a char array

Question

I have seen many similar questions but none that seem to be working for my code, I think I am overlooking something basic, maybe you can help.

Right now I'm constructing a string to be sent as a request to the winsock send function, which requires a char [] to be sent. I need to convert my std::string into a char array (char []).

Currently this is the request that works:

char request [] = "GET /gwc/cgi-bin/fc?client=udayton0.1&hostfile=1HTTP/1.0\nHost:www.gofoxy.net\n\n";

But I need to change a string of a request to the same data structure.

I appreciate any help!

edit:

I can convert a string to a char *, but how can I use that to get a character array? I hope I'm not making it more confusing. Here are two attempts that produce char star's that aren't compatible with the send request when I run:

//convert request into a char[]
//char *req_ch = new char[req_str.size()+1];
//hostCh[req_str.size()] = 0;
//memcpy(req_ch, req_str.c_str(), req_str.size());

//char * req = new char[req_str.size() +1];
//std::copy(req_str.begin(), req_str.end(), req);
//req[req_str.size()] = '\0';

Isn't c_str() what you are looking for, which returns a pointer? — Richard J. Ross III
– Richard J. Ross III, Commented Sep 11, 2012 at 1:52
So a string to non-const character array? I'd go for a vector constructed with iterators and using vector::data(). — Qaz
– Qaz, Commented Sep 11, 2012 at 1:52
@gosly, An array will decay to a pointer when passed into a function, so it doesn't matter if you pass in a pointer. — Qaz
– Qaz, Commented Sep 11, 2012 at 2:04

Brian Neal · Accepted Answer · 2012-09-11 02:05:55Z

8

If you have some legacy C-style API with a signature like this, where it is expecting a null terminated C-style string:

void foo(const char* data);

then you can typically do something like:

std::string s("my string data");
foo(s.c_str());

If you really need an array, or a non-const version of the data, so that the API is this:

void foo(char* data, std::size_t len);  // or foo(char[] data, std::size_t len);

Then you could do something like this:

std::string s("my string data");
std::vector<char> v(s.begin(), s.end());
foo(&v[0], v.size());    // or foo(v.data(), v.size()); in C++11

answered Sep 11, 2012 at 2:05

Brian Neal

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Edward Strange · Accepted Answer · 2012-09-11 01:56:48Z

2

Do you really need char[] or will char const* do?

If the latter, c_str() will do what you want.

If the former then you'll need to copy the string into something that does what you want:

std::vector<char> buff(str.size() + 1); // initializes to all 0's.
std::copy(str.begin(), str.end(), buff.begin());
fun_call(&buff[0]);

Chances are that you only need the c_str version. If you're needing this second version then you're reading and probably, hopefully, providing a buff max size.

answered Sep 11, 2012 at 1:56

Edward Strange

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2 Comments

Qaz Over a year ago

Just construct the vector with str.begin(), str.end() (or std::begin and std::end). Since C++11, it also has data(), which is meant for accessing the pointer.

Edward Strange Over a year ago

It'd be interesting to see which is faster what with needing to append a '\0'. An improvement to both might be to use str.c_str(), str.c_str() + str.size + 1.

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