Actually reading the newline

[luc atlis]

Currently I'm having problems reading input files. The problem I'm encountering is that I actually want to read the newline character instead of using it as a delimiter.

After doing some testing it looks like std::getline, which I'm using with an ifstream, reads the newline and puts it in the string as follows: "\\n ". Does anyone know why this is happening? And more importantly how I should read the newline so that it still works like a newline in the resulting string.

I think the problem is pretty self explanatory, if you'd like to see some code containing the problem please say so, then I'll post my code.

[Janlan]

Post your code 'till now.

[luc atlis]

std::ifstream is(filename.c_str(), std::ios::in);
intermediate_mapper_format::source s;
int line_number = 1;
while(!is.eof()) {
	//Get the tag name, which is first part before the separator
	std::string name;
	std::getline(is, name, ',');
	boost::algorithm::trim(name);

	//Get the value
	std::string value;
	char c = is.peek();
	//Skip possible white space
	while(c == ' ') {
		is.ignore(1);
		c = is.peek();
	}
	if (c == '\'' || c == '"') {
		//If it starts with ' or " then we should also copy \n characters that are within the parenthesis pair
		std::string partial_value;
		is.ignore(1);
		bool done = false;
		do {
			std::getline(is, partial_value, c);
			//Check if we're done or if the '/" has another occurence in the value
                        if ('\n' == is.peek()) {
				is.ignore(1);
				value += partial_value;
				done = true;
			} else {
				value += partial_value;
				value += c;
			}
		} while (!done);
	} else {
		std::getline(is, value);
	}

	//Add the name and value to the source format
	intermediate_mapper_format::source::iterator i = s.find(name);
	if (i != s.end()) {
		intermediate_mapper_format::tag_values tvs = i->second;
		tvs.push_back(std::make_pair(line_number, value));
	} else {
		intermediate_mapper_format::tag_values tvs;
		tvs.push_back(std::make_pair(line_number, value));
		s.insert(std::make_pair(name, tvs));
	}
	line_number++;
}
intermediate_mapper_format::name_description nd;
m_imf = intermediate_mapper_format_ptr(new intermediate_mapper_format(s, nd));
is.close();

Here's the code. To give a bit more background information, it is used to parse CSV files which contain per line a name and value. However if the value starts with ' or " it is possible to have large pieces of text containing newlines. I've tested this with a CSV with the following lines:

naam, "individual model 1"
omschrijving,'raar
vreemd's
lelijke omschrijving'
puntjes,101 

I've got a work around where I replace "\\n " with "\n" which works, but is ofcourse an ugly solution.

[bartoli]

'\n' in memory is represented by '\\n' in C code, because by default, when the Compiler will see \ in a string, it will not handle it as a normal char, instead it will look at the next character to find a special haractert code (like \n for example :-P ). That means that the '\' char has to be written '\\' in a C code string, giving '\\n' in C code for '\n' in memory

[luc atlis]

'\n' in memory is represented by '\\n' in C code, because by default, when the Compiler will see \ in a string, it will not handle it as a normal char, instead it will look at the next character to find a special haractert code (like \n for example :-P ). That means that the '\' char has to be written '\\' in a C code string, giving '\\n' in C code for '\n' in memory

That would be the case if I was reading my input from memory. I'm reading from a file, so this should not be the case.

[zb0S216C]

luc atlis wrote:

That would be the case if I was reading my input from memory. I'm reading from a file, so this should not be the case.

When a file is opened, it's loaded into memory. In a sense, you're reading from memory.

_wazzak

[luc atlis]

Ok, so if I understand this correctly. Whenever you read from a file and you read the newline and don't discard it, you never end up with an actual newline character and what I want to do is impossible.

On a sidenote, I understand why this would give me a "\\n" where there should be a newline. But why does it also add another space? I'm ending up with "\\n " where a newline is encountered in the input file.

[bartoli]

You still have the solution of reading your file in binary mode, you'll get a unique string containing the whole file, with the new lines (encoded as CR or CR+LF depending on your system), then manually looking for the lines

[luc atlis]

Well, then I'm sticking with my ugly solution. Thanks everybody for the help. At least I learned some more about reading files.

[S6k9GNh0]

Most people don't even use delimiters. They'll read the file entirely into memory and parse it using some algorithm (which may use delimiters), turning it into something useful...