[solved]problems trying to read from a file

[vblanco]

Hello, im trying to learn how to read/write files, so im trying to make a simple .OBJ loader (i dont want to just copypaste, i want do to it myself to learn) the problem is that the file is opened , myfile.is_open() returns true correctly, but then, when i try to getline, it doesnt work, and if i search in debug mode, the Ifstream object says "error reading characters of string" . im learning to handle files, but that gets in my way so i cant do anything, if someone knows what error im making, please help me ( i searched in google for the error, but got no useful answer)
the code is

Code: Select all

#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <string>
using namespace std;

void LoadOBJ(const char* file,bool Log)
{
	printf(file);
	string line;
	ifstream myfile (file);
	if (myfile.is_open())
	{
		while ( true)
		{
			if(getline (myfile,line)  )
			{
			cout << line << endl; // currently i print the lines to the screen for testing, later ill add the parsisng code
			}
			else
			{
				break;
			}
		}
    
	}
	else
	{
		printf("error in opening file");
	}
	myfile.close();
}


int main()
{
	

	LoadOBJ("SimpleCube.obj",true);

	while(true)
	{
	}
}

that while(true) at the end is a hack to force the command window to not auto close, i know its really lame.
the SimpleCube.obj file its on the same folder as the executable and its the default cube exported from blender with the obj exporter.

[Faranwath]

Binary files have no concept of line, I would say. All they contain is a bunch of bytes that a text editor interprets as characters, so you cannot say "Give me the first line of this binary file".
Try this out:

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#include <fstream>
#include <string>
#include <algorithm>
#include <iterator>
/* ... */
std::string file_contents;
std::ifstream stream{file_name, std::ios::binary};
if (!stream.is_open())
    /* handle error */
else
{
    std::copy(
        std::istreambuf_iterator<char>{stream},
        std::istreambuf_iterator<char>{},
        std::back_inserter(file_contents)
        );
}

[vblanco]

But the .obj is a text based file format, you can open it with notepad++ just like any text file and its nicely formatted in lines, and normal characters. i know the difference beetween binary and text files., in fact, the OBJ im testing with is this

Code: Select all

# Blender v2.66 (sub 1) OBJ File: ''
# http://www.blender.org
mtllib SimpleCube.mtl
o Cube
v 1.000000 -1.000000 -1.000000
v 1.000000 -1.000000 1.000000
v -1.000000 -1.000000 1.000000
v -1.000000 -1.000000 -1.000000
v 1.000000 1.000000 -0.999999
v 0.999999 1.000000 1.000001
v -1.000000 1.000000 1.000000
v -1.000000 1.000000 -1.000000
usemtl Material
s off
f 1 2 3 4
f 5 8 7 6
f 1 5 6 2
f 2 6 7 3
f 3 7 8 4
f 5 1 4 8

[Faranwath]

Oh well, my bad... I'm not familiar at all with the format, the name suggested me it was binary-based. In that case, your code should work Try reading a different file, or a subset of the one you're working with (e.g. the first two lines). If that fails, look for an error in a more broader context. Just to be sure, is the name of the file correctly spelled?

[vblanco]

the name is correct, if i put it wrong, to a file that doesnt exists, the if (myfile.is_open()) returns false, and closes the program. but it returns true, but cant read the file, its a bit like WTF
edit: got fixed by just copying the file (?????????) and renaming it

[Faranwath]

Well, in that case I don't really know what to say. Maybe the file has some weird attributes (i.e. "thou shalt not read me!").
Let's see, you said you were learning, so create a text file containing a bunch of lines, and do the following:

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#include <iostream>
#include <fstream>
#include <string>

int main()
{
    std::ifstream file{"my_file.txt"};
    if (!file.is_open())
    {
        std::cerr << "oops!\n";
        return 1;
    }

    std::string line;
    while (std::getline(file, line))
        std::cout << line << std::endl;
}

This has to work, no questions.

edit: We'll never know then

[vblanco]

ill mark it as solved, anyway, i MADE MY OBJ LOADER, i feel so proud of myself.