Need help loading simple text data with c++ - c++

Question

I need help loading a custom file format into my program made in c++...
I know there's a simple way of doing this but I think I'm using the
wrong terms to search for it online...
My custom format for 3d objects is as follows:
NumVerts 6
//verts (float)
-1
-1
0
1
-1
0
-1
1
0
1
-1
0
1
1
0
-1
1
0
//texture (float)
0
0
1
0
0
1
1
0
1
1
0
1
//index (int)
0
1
2
1
3
2
And that is a quad... (yeas; I know... horrible format... but it's what I'm using for an android game).
I want to make a function in c++ for my editor (SDL + OpenGL for windows) that loads these files into data... Unfortunately though I know how to export this format with C++, I can't figure out how to import them... I wish to use the fstream commands...
If someone could quickly write out a simple version I'd be really thankful.
I just it to do the following:
Find text file from input string
read "NumVerts" and grab the integer written after it
loop through the next (NumVerts*3) lines and grab each number as a float
loop though the next (NumVerts*2) lines and grab each number as a float
loop through the next (NumVerts*1) lines and grab each number as an Int
(skip any line that starts with "//")
close file.
Thank you for reading and any help would be really good right now... or a relivent link that is quite simple and reads strings from files and grabs numbers from them to be placed into memory...
I really just want to finish this game and it's getting really stressful trying to locate helpful tutorials.
Update: updated the script... I accidently forgot to seperate 1's and 0's...

Answer 1

Hope this helps. Incidentally, you have the wrong number of vertex components - you need 18 of them.
#include <algorithm>
#include <exception>
#include <fstream>
#include <iostream>
#include <string>
#include <vector>
#include <boost/algorithm/string/trim.hpp>
#include <boost/lexical_cast.hpp>
using boost::lexical_cast;
int load_3d_object(const std::string& filename,
std::vector<float>& vertComponents,
std::vector<float>& texComponents,
std::vector<int>& indices)
{
std::ifstream fs(filename.c_str());
std::string line;
if(!std::getline(fs, line))
{
throw std::runtime_error("The input file is empty");
}
if(line.substr(0,8) != "NumVerts")
{
throw std::runtime_error("The first line must start with NumVerts");
}
// Extract the number of vertices.
int numVerts = lexical_cast<int>(line.substr(line.find(' ') + 1));
// Read in the vertex components, texture components and indices.
while(std::getline(fs, line))
{
boost::trim(line);
if(line.substr(0,2) == "//") continue;
if((int)vertComponents.size() < numVerts * 3) vertComponents.push_back(lexical_cast<float>(line));
else if((int)texComponents.size() < numVerts * 2) texComponents.push_back(lexical_cast<float>(line));
else indices.push_back(lexical_cast<int>(line));
}
return numVerts;
}
int main()
{
std::vector<float> vertComponents;
std::vector<float> texComponents;
std::vector<int> indices;
try
{
int numVerts = load_3d_object("input.txt", vertComponents, texComponents, indices);
}
catch(std::exception& e)
{
std::cout << e.what() << '\n';
}
return 0;
}

Answer 2

Hopefully this might help (minimal error checking):
int _get_num_verts_value(std::ifstream& a_in)
{
char buf[128];
int result = -1;
a_in.getline(buf, sizeof(buf));
while (a_in.good())
{
if (a_in.gcount() > 9)
{
string s(buf);
if (0 == s.find("NumVerts "))
{
result = atoi(s.substr(8).c_str());
break;
}
}
a_in.getline(buf, sizeof(buf));
}
return result;
}
template <typename T>
void _get_values(std::ifstream& a_in, std::vector<T>& a_values)
{
char buf[128];
a_in.getline(buf, sizeof(buf));
int i = 0;
while (a_in.good())
{
string line(buf);
if (0 != line.find("//"))
{
a_values[i++] = boost::lexical_cast<T>(line);
// All read ?
if (i == a_values.capacity())
{
break;
}
}
a_in.getline(buf, sizeof(buf));
}
}
int main(int /*a_argc*/, char** /*a_argv*/)
{
ifstream in("test.txt");
const int num_verts_value = _get_num_verts_value(in);
std::vector<float> verts(num_verts_value * 3);
_get_values<float>(in, verts);
std::vector<float> textures(num_verts_value * 2);
_get_values<float>(in, textures);
std::vector<int> indexes(num_verts_value);
_get_values<int>(in, indexes);
in.close();
return 0;
}

Answer 3

using a flat file for this purpose could be a bad idea. it's pretty fragile. I prefer to a binary file or a self-described file (e.g xml).
std::ifstream in("in");
char buf[256];
std::string line;
int NumVerts;
in >> buf >> NumVerts;
std::vector<float> verts(NumVerts * 3);
std::getline(in, line);//read the rest of the line
std::getline(in, line);//skip the comment line
std::for_each(verts.begin(), verts.end(), [&in](float& par){
in >> par;
});
std::vector<float> texture(NumVerts * 2);
std::getline(in, line);//read the rest of the line
std::getline(in, line);//skip the comment line
std::for_each(texture.begin(), texture.end(), [&in](float& par){
in >> par;
});
std::vector<int> index(NumVerts);
std::getline(in, line);//read the rest of the line
std::getline(in, line);//skip the comment line
std::for_each(index.begin(), index.end(), [&in](int& par){
in >> par;
});

Answer 4

For the links on how to DIY:
Tutorial: http://www.cplusplus.com/doc/tutorial/files/
Reference: http://new.cplusplus.com/reference/iostream/fstream/
Example code:
#include <string>
#include <iostream> // needed for printing stuff out
#include <fstream> // Needed to read the file
#include <stdexcept>
#include <vector>
using namespace std;
struct Vertice {
double x,y,z; // 3 part stuff to read
double a,b; // 2 part stuff to read
int i; // 1 int thing to read
};
/// Reads a number ignoring comment lines (and any other line that isn't a number)
template <typename T>
T readNumber(istream& data) {
char lastChar;
while (data.good()) {
data >> lastChar; // Don't use peek as that won't skip whitespace
data.putback(lastChar);
if (( (lastChar >= '0') && (lastChar <= '9') ) || (lastChar == '-')) {
// If we're looking at a number read and return it
T result;
data >> result;
return result;
} else {
// If it's not part of a number .. assume it's a comment line and skip the whole line
string commentLine;
getline(data, commentLine);
// TODO: Maybe just skip '//' lines and throw an exception for everything else..
}
}
throw exception("Couldn't read file");
}
double readDouble(istream& data) { return readNumber<double>(data); }
int readInt(istream& data) { return readNumber<int>(data); }
int main(int argc, char** argv) {
if (argc != 2)
cout << "Usage: " << argv[0] << " [DATA_FILE_NAME]" << endl;
else {
fstream data(argv[1], ios_base::in);
data >> skipws; // Skip whitespace
string lastString;
long numVerts = -1;
// Read in words ignoring everything until we hit a 'NumVerts'
while (numVerts < 0) {
data >> lastString;
if (lastString == "NumVerts")
data >> numVerts;
}
// We know how many to get now
typedef vector<Vertice> Verts;
Verts verts(numVerts);
// Read in the triples
for (Verts::iterator i=verts.begin(); i != verts.end(); ++i) {
i->x = readDouble(data);
i->y = readDouble(data);
i->z = readDouble(data);
}
// Read in the pairs (some other data)
for (Verts::iterator i=verts.begin(); i != verts.end(); ++i) {
i->a = readDouble(data);
i->b = readDouble(data);
}
// Read in the single integer value
for (Verts::iterator i=verts.begin(); i != verts.end(); ++i) {
i->i = readInt(data);
}
// Print out all we found
for (Verts::iterator i=verts.begin(); i != verts.end(); ++i) {
cout << "Vertice" << endl
<< " x: " << i->x << endl
<< " y: " << i->y << endl
<< " z: " << i->z << endl
<< " a: " << i->a << endl
<< " b: " << i->b << endl
<< " i: " << i->i << endl
<< endl;
}
}
}
The example code throws an error on the provided files as there isn't enough data to fill out the 'NumVerts'.