RapidXML, reading and saving values - c++

Question

I've worked myself through the rapidXML sources and managed to read some values. Now I want to change them and save them to my XML file:
Parsing file and set a pointer
void SettingsHandler::getConfigFile() {
pcSourceConfig = parsing->readFileInChar(CONF);
cfg.parse<0>(pcSourceConfig);
}
Reading values from XML
void SettingsHandler::getDefinitions() {
SettingsHandler::getConfigFile();
stGeneral = cfg.first_node("settings")->value();
/* stGeneral = 60 */
}
Changing values and saving to file
void SettingsHandler::setDefinitions() {
SettingsHandler::getConfigFile();
stGeneral = "10";
cfg.first_node("settings")->value(stGeneral.c_str());
std::stringstream sStream;
sStream << *cfg.first_node();
std::ofstream ofFileToWrite;
ofFileToWrite.open(CONF, std::ios::trunc);
ofFileToWrite << "<?xml version=\"1.0\"?>\n" << sStream.str() << '\0';
ofFileToWrite.close();
}
Reading file into buffer
char* Parser::readFileInChar(const char* p_pccFile) {
char* cpBuffer;
size_t sSize;
std::ifstream ifFileToRead;
ifFileToRead.open(p_pccFile, std::ios::binary);
sSize = Parser::getFileLength(&ifFileToRead);
cpBuffer = new char[sSize];
ifFileToRead.read( cpBuffer, sSize);
ifFileToRead.close();
return cpBuffer;
}
However, it's not possible to save the new value. My code is just saving the original file with a value of "60" where it should be "10".
Rgds
Layne

Answer 1

I think this is a RapidXML Gotcha
Try adding the parse_no_data_nodes flag to cfg.parse<0>(pcSourceConfig)

Answer 2

You should definitely be testing that the output file opened correctly and that your write succeeded. At the simplest, you need something like:
if ( ! ofFileToWrite << "<?xml version=\"1.0\"?>\n"
<< sStream.str() << '\0' ) {
throw "write failed";
}
Note that you don't need the '\0' terminator, but it shouldn't do any harm.

Answer 3

Use the following method to add an attribute to a node. The method uses the allocation of memory for strings from rapidxml. So rapidxml takes care of the strings as long as the document is alive. See http://rapidxml.sourceforge.net/manual.html#namespacerapidxml_1modifying_dom_tree for further information.
void setStringAttribute(
xml_document<>& doc, xml_node<>* node,
const string& attributeName, const string& attributeValue)
{
// allocate memory assigned to document for attribute value
char* rapidAttributeValue = doc.allocate_string(attributeValue.c_str());
// search for the attribute at the given node
xml_attribute<>* attr = node->first_attribute(attributeName.c_str());
if (attr != 0) { // attribute already exists
// only change value of existing attribute
attr->value(rapidAttributeValue);
} else { // attribute does not exist
// allocate memory assigned to document for attribute name
char* rapidAttributeName = doc.allocate_string(attributeName.c_str());
// create new a new attribute with the given name and value
attr = doc.allocate_attribute(rapidAttributeName, rapidAttributeValue);
// append attribute to node
node->append_attribute(attr);
}
}