Getline Function Problem

**neutral87** · 06-04-2013

Hi all,

I have written a C++ program I have multiple of CSV file used as input, which I open one at a time and close it after extracting data to a output file which is the only file.

I run getline(inFile,line);
outFile << line << endl;

I run this code, and only part of it is goes to the output file I got, also have spacing randomly to specific file and inconsistent

But when I slower the code, like system("Pause") in the loop, I can get extract what I want perfectly....

Is my program running to fast, why getline would be skipping part of what things I want?

I really have no idea where the problem is coming from, or where to start

Many Thanks!

**jimblumberg** · 06-04-2013

Is my program running to fast,

No.

why getline would be skipping part of what things I want?

Without seeing your code I have no idea.

I suggest you post the relevant code, a sample of your input files. And then show us what the code you provide is producing and your desired output.

Jim

**neutral87** · 06-04-2013

Hi Jim,

Thanks for your reply

I have a sample of my code, as you can see I have specific Datalength of where the place should start to getline for specific data I would like to extract

For example, the datalength for a specific data is 240, but the output file will just grab 150 of the 240, but it is correct where the getline starts

I have about 100+ CSV file containing, Date, Open, High, Low, Close Just standard price data

Originally Posted by jimblumberg

No.

Without seeing your code I have no idea.

I suggest you post the relevant code, a sample of your input files. And then show us what the code you provide is producing and your desired output.

Jim

Code:

	if (dataname[i] == dataname)
	{
		inFile.seekg(datalength[i], ios::beg);
		for (int j = 0; j < datacount[i]; j++)
		{
			getline(inFile, line);
			outFile << line << endl;
		}
		
	}

And I do this for multiple files from use case 0 - Case 300 etc

**neutral87** · 06-04-2013

I'm sure it is a kind of memory leak....

Or is it using vector pushback and then output is the safer approach

But how to outfile using vector which I don't know how to use

**grumpy** · 06-05-2013

No, it is not a memory leak.

seekg() is generally used on streams opened in binary mode. getline() is generally used on streams opened in non-binary (aka text) mode.

Either way, using them together can give results like you describe. The solution: don't use them both on the same stream.

**neutral87** · 06-05-2013

Grumpy!! u are the man!! Thanks!!

Just want to know how can I use in different stream?

Can I put the result in array then at different stream output it back that way? Meaning one is void and another in main?

Originally Posted by grumpy

No, it is not a memory leak.

seekg() is generally used on streams opened in binary mode. getline() is generally used on streams opened in non-binary (aka text) mode.

Either way, using them together can give results like you describe. The solution: don't use them both on the same stream.

**Elkvis** · 06-05-2013

since you're writing to the file, seekg will not do what you expect anyway. it moves the "get" pointer (hence the 'g'), whereas seekp moves the "put" pointer.

**neutral87** · 06-05-2013

What do you mean? I don't get it, what you mean it doesn't work?

**neutral87** · 06-05-2013

seekg goes with ifstream and/or fstream objects to move about within the file for reading.

seekp goes with ofstream and/or fstream objects to move about within the file for writing.

Why would I need seekp?

**Elysia** · 06-06-2013

One possibility: To move backwards in the file, for example to overwrite some data.
Another possibility: If the OS allows it, you can seek beyond the end of the file and write there to automatically create a big file without having to fill it with garbage data. Useful for preallocation.

**neutral87** · 06-06-2013

Hi Elysia

Thanks for your reply.

I research these few past days, some people saying seekg() is used too often, and its not really good

A better way is read the whole buffer and skipping the buffer, but this is really complicated, if anyone know it really works, I will move towards this direction.

In the meantime, the problem of the output file is really consistent, the problem output is generated the same each time, the spacing is about 227 line each time for some data extracted from different files

Code:

char buffer[52];for (int i=0;i<n;i++) {    fid.read(buffer, sizeof(buffer));    memcpy(&x[i], &buffer[4], sizeof(x[i]));    memcpy(&y[i], &buffer[20], sizeof(y[i]));    // etc}

Code:

Last point

if (dataname[i] == dataname)
{
    inFile.seekg(datalength[i], ios::beg);
    for (int j = 0; j < datacount[i]; j++)
    {
        getline(inFile, line);
        outFile << line << endl;
    }
     system("Pause"); <---------------(If add this and press enter myself, the data is accurate and no spacing..... I don't get it!!"
}

Originally Posted by Elysia

One possibility: To move backwards in the file, for example to overwrite some data.
Another possibility: If the OS allows it, you can seek beyond the end of the file and write there to automatically create a big file without having to fill it with garbage data. Useful for preallocation.

**jimblumberg** · 06-06-2013

Please show a small complete program that illustrates your problem. Also post what you input into the program, and provide a small sample input file. Then show an example of the output your program is producing and what the desired output should be.

Jim

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