Having a string how to get its contents from first `/r/n/r/n` until 2 lines from string end? - c++

Question

I try to create simple file upload service in C++. I get all user request body as one big string. User can upload any type of data. I need to get only user file contents from request boby string.
so for example now I have next code working with my service API provider:
std::cout << "Request body: " << request->body << std::endl << "Request size: " << request->body.length() << std::endl;
and this would print as:
Request body: ------WebKitFormBoundaryAZlJcLinxYi6OCzX
Content-Disposition: form-data; name="datafile"; filename="crossdomain.xml"
Content-Type: text/xml
я╗┐<?xml version="1.0"?>
<!DOCTYPE cross-domain-policy SYSTEM "http://www.macromedia.com/xml/dtds/cross-
omain-policy.dtd">
<cross-domain-policy>
<allow-access-from domain="*" to-ports="*" />
</cross-domain-policy>
------WebKitFormBoundaryAZlJcLinxYi6OCzX--
Request size: 411
So I need to get from request->body (which is string) all data from first /r/n/r/n until last line -2 lines. How to do such thing with string in C++?

Answer 1

This isn't the most elegant approach, but one option would be to do something like this:
std::string contents = /* ... get the string ... */
/* Locate the start point. */
unsigned startPoint = contents.find("\r\n\r\n");
if (startPoint == string::npos) throw runtime_error("Malformed string.");
/* Locate the end point by finding the last newline, then backing up
* to the newline before that.
*/
unsigned endPoint = contents.rfind('\n');
if (endPoint == string::npos || endPoint == 0) throw runtime_error("Malformed string.");
endPoint = contents.rfind('\n', endPoint - 1);
if (endPoint == string::npos) throw runtime_error("Malformed string.");
/* Hand back that slice of the string. */
return std::string(contents.begin() + startPoint, contents.begin() + endPoint);

Answer 2

You can use regular expressions for that. This page has some nice c++ examples: http://www.math.utah.edu/docs/info/libg++_19.html