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Jun 14th, 2009

Re: Problem with ifstream returning fail()

Thanks.

Everyone knows that differences and they could program accordingly.

adatapost

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Jun 14th, 2009

Re: Problem with ifstream returning fail()

I just got back from work and looked at the zip file you posted.

The program fails when function dummy() calls FileToString() because the file name (first parameter) contains the '\n' at the end of the filename, so the os can't find that file.

To correct that you will have to modify function Tokenize() to strip the character from the string.

(Toggle Plain Text)

vector<string> Tokenize(string data, char delimiter)
{
	vector<string> pieces;
	unsigned int a = 0;
	unsigned int b;
	while (true)
	{
		b = (unsigned int)(data.find(delimiter, a));
		if (b == string::npos)
			break;
                pieces.push_back( data.substr(a, b - a-1)); 
		a = b + 1;
	}
	pieces.push_back(data.substr(a));
	return pieces;
}

Last edited by Ancient Dragon; Jun 14th, 2009 at 2:13 am.

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Jun 14th, 2009

Re: Problem with ifstream returning fail()

The wittingly wrong statement in OP code is delete buffer; - must be delete[]buffer; . Yet another defect: insufficient error check-up.

C++ Syntax (Toggle Plain Text)
long GetFileSize(ifstream &file)
{
    static const streamoff badPos(-1);
    if (!file)  // test added
        return -1;
    streamoff temp = file.tellg();
    if (temp != badPos && file.seekg(0L, ios::end)) {
        streamoff end = file.tellg();
        if (end != badPos && file.seekg(temp, ios::beg))
            return static_cast<long>(end);
    }
    return -2;
}
 
/// Load the file to fileS string, return filesize. 
/// Non-positive returned if failed
long FileToString(const string &file_path, string &fileS)
{
	ifstream input(file_path.c_str(), ios::binary);
    if (!input) { // simple and clear stream state test
        fileS.clear(); // no contents
        return -1;
    }
	long size = GetFileSize(input);
    if (size <= 0) { // filesize test added.
        fileS.clear();
        return -2;
    }
	char* buffer = new char[size];
    if (input.read(buffer, size)) {
        fileS.reserve(size+size/10); // add reserve
	    fileS.assign(buffer, size);
    } else {
        size = -3;
    }
	delete [] buffer; // [] inserted!
	//input.close(); // no need: let destructor works
	return size;
}
long GetFileSize(ifstream &file)
{
    static const streamoff badPos(-1);
    if (!file)  // test added
        return -1;
    streamoff temp = file.tellg();
    if (temp != badPos && file.seekg(0L, ios::end)) {
        streamoff end = file.tellg();
        if (end != badPos && file.seekg(temp, ios::beg))
            return static_cast<long>(end);
    }
    return -2;
}

/// Load the file to fileS string, return filesize. 
/// Non-positive returned if failed
long FileToString(const string &file_path, string &fileS)
{
	ifstream input(file_path.c_str(), ios::binary);
    if (!input) { // simple and clear stream state test
        fileS.clear(); // no contents
        return -1;
    }
	long size = GetFileSize(input);
    if (size <= 0) { // filesize test added.
        fileS.clear();
        return -2;
    }
	char* buffer = new char[size];
    if (input.read(buffer, size)) {
        fileS.reserve(size+size/10); // add reserve
	    fileS.assign(buffer, size);
    } else {
        size = -3;
    }
	delete [] buffer; // [] inserted!
	//input.close(); // no need: let destructor works
	return size;
}

About wrong filelist parsing (adatapost's tip):

If you want a portable code, never use FileToString to load line-oriented filelist file. It's the case where binary (low-level) stream/string processing is an absolutely irrelevan method. The old good std::getline is the best and the portable tool to "tokenize" a simple text file!

By the way, never add non-inline function definitions in .h files! Have you ever heard about separate compilation? Only function prototypes are placed in .h files.

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Jun 14th, 2009

Re: Problem with ifstream returning fail()

First, sorry for the late response. I was sleeping and forgot to mention it in the last post.

@Ancient Dragon: I kind of get what you are saying because the file names do contain things like '\n' or '\r' in them, but your change to the Tokenize function breaks its generic functionality. This code doesn't work correctly:

c++ Syntax (Toggle Plain Text)
int main()
{
 
	vector<string> temp = Tokenize("blah;blah;blah;blah;", ';');
	for (int i = 0; i < temp.size(); i++)
	{
		cout << temp[i] << endl;
	}
 
	return 0;
}
int main()
{

	vector<string> temp = Tokenize("blah;blah;blah;blah;", ';');
	for (int i = 0; i < temp.size(); i++)
	{
		cout << temp[i] << endl;
	}

	return 0;
}

But, I get what you mean by having to take those \r or \n out of my file names.

@ArkM: Thanks for going through my code. But, I am a bit confused about some of your fixes:
1. At line 31, why do I need to reserve size + size/10 ? Shouldn't it just be size ?
2. For FileToString , I was thinking of just returning the error code and not the file size because I can just do fileS.size() . Is this a bad programming habit on my part?

Thanks all. I "approve" of all your posts :D (reputation)

CppFTW

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Jun 14th, 2009

Re: Problem with ifstream returning fail()

1. Well, reserve size (if no need in some postprocessing)
2. Tastes differs; for example, I prefer to return bool in such cases. I think, returned size if more useful than 0. Moreover, zero on success is not a natural code, look at:

C++ Syntax (Toggle Plain Text)
if (!FileToString(...)) { // Haha, if NOT means SUCCESS
if (!FileToString(...)) { // Haha, if NOT means SUCCESS

ArkM

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Jun 14th, 2009

Re: Problem with ifstream returning fail()

Okay.

Thanks all. I understand why I was getting my problem now and also was able to fix some more problems in my code.

CppFTW

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Jun 15th, 2009

Re: Problem with ifstream returning fail()

Click to Expand / Collapse Quote originally posted by CppFTW ...

Okay.

Thanks all. I understand why I was getting my problem now and also was able to fix some more problems in my code.

If so, mark this thread as solved

ArkM

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Jun 15th, 2009

Re: Problem with ifstream returning fail()

Okay, done.

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