I have tool that creates variables for a simulation. The current workflow involves hand copying those variables into the simulation input file. The input file is a standard flat file, i.e. not binary or XML. I would like to automate the addition of the variables to the flat input file.
The variables copy over existing variables in the file, e.g.
New Variables:
Length 10
Height 20
Depth 30
Old Variables:
...
Weight 100
Age 20
Length 10
Height 20
Depth 30
...
Would like to have the old variables copy over the new variable. They are 200 lines into the flat input file.
Thanks for any insights.
P.S. This is on Windows.
If you're stuck using flat, then you're stuck using the old fashioned way of updating them: read from original, write to temp file, either write the original row or change the data and then write that. To add data, write it to the temp file at the appropriate point; to delete data, simply don't copy it from the original file.
Finally, close both files and rename the temp file to the original file name.
Alternatively, it might be time to think about a little database.
For something like this I'd be looking at a simple template engine. You'd have a base template with predefined marker tokens instead of variable values and then just pass the values required to your engine along with the template and it will spit out the resultant file, all present and correct. There are a number of Open Source template engines available in Java that would meet your needs, I imagine such things are also available in your language of choice. You could even roll your own without too much difficulty.
Note that under Unix, one would probably look at using mmap() because you can then use functions such as memmove() to move the data around and add new data or truncate() the result if the file is then smaller (you may also want to use truncate() to grow the file).
Under MS-Windows, you have the MapViewOfFileEx() function to do the same thing. The API is different, though,
and I'm not exactly sure what happens or how to grow/shrink the file (MSDN also includes a truncate()-like function and maybe that works).
Of course, it's important to use memcpy() or memmove() properly to not overwrite the wrong data or go outside the buffer.
Related
I have a file that can be opened thru notepad application.
Basically, this file(which can be opened thru notepad) is created by a software and that software uses the values inside that file to run. You can edit the values inside the file using its software.
I just want specific lines(values) to be restricted from being edited because I am implementing strict values inside that file that no one will be able to edit except me.
Is there any clever way to restrict specific lines inside that file from being edited?
I tried the basic way - I used the change permission read/write on that file but I can't change ANY values inside the file which is undesirable.
Note: I have very little to no experience about python, c++, or java but any suggestion will give me idea to learn from it.
Edit:
Here's an example inside the file:
[Type Data]
Comment=Standard Dispense
[Shared_A]
802=1
807=750
11=0
12=0
.
What I want is restrict the value from row/column "807" which is equal to number 750.
I want this number 750 not to be edited even from the software so that other people will not mess it up. I want to set this value as standard value.
Is there any program that you can write inside that file so that it cannot be edited from the software unless I open that file and edit it?
I work from a production/manufacturing company that uses the software that is used for dispensing.
A text file is simply a sequence of bytes that represent code units to encode code points in any given character set. Every byte value is a potentially legal character encoding, leaving no values to encode additional semantics (like guard regions).
With that it should be obvious that there is nothing you can do to partially limit editing of a file using a standard text editor. Whatever problem you are trying to solve, this is not a solution. Next time around you might want to ask about the problem you are trying to solve rather than your proposed solution.
Are there any rules for file extensions? For example, I wrote some code which reads and writes a byte pattern that is only understood by that specific programm. I'm assuming my anti virus programm won't be too happy if I give it the name "pleasetrustme.exe"... Is it gerally allowed to use those extensions? And what about the lesser known ones, like ".arw"?
You can use any file extension you want (or none at all). Using standard extensions that reflect the actual type of the file just makes things more convenient. On Windows, file extensions control stuff like how the files are displayed in Windows Explorer and what happens when you double click on it.
I wrote some code which reads and writes a byte pattern that is only
understood by that specific programm.
A file extension is only an indication of what type of data will be inside, never a guarantee that certain data formatted in a specific way will be inside the file.
For your own specific data structure it is of course always best to choose an extension that is not already in use for other file formats (or use a general extension like .dat or .bin maybe). This also has the advantage of being able to use an own icon without it being overwritten by other software using the same extension - or the other way around.
But maybe even more important when creating a custom (binary?) file format, is to provide a magic number as the first bytes of that file, maybe followed by a file header structure containing a version number etc. That way your own software can first check the header data to make sure it's the right type and version (for example: anyone could rename any file type to your extension, so your program needs to have a way to do some checks inside the file before reading the remaining data).
Seems like it must be easy, but I just can't figure it out. How do you delete the very last character of a file using Ruby IO?
I took a look at the answer for deleting the last line of a file with Ruby but didn't fully understand it, and there must be a simpler way.
Any help?
There is File.truncate:
truncate(file_name, integer) → 0
Truncates the file file_name to be at most integer bytes long. Not available on all platforms.
So you can say things like:
File.truncate(file_name, File.size(file_name) - 1)
That should truncate the file with a single system call to adjust the file's size in the file system without copying anything.
Note that not available on all platforms caveat though. File.truncate should be available on anything unixy (such as Linux or OSX), I can't say anything useful about Windows support.
I assume you are referring to a text file. The usual way of changing such is to read it, make the changes, then write a new file:
text = File.read(in_fname)
File.write(out_fname, text[0..-2])
Insert the name of the file you are reading from for in_fname and the name of the file you are writing to for 'out_fname'. They can be the same file, but if that's the intent it's safer to write to a temporary file, copy the temporary file to the original file then delete the temporary file. That way, if something goes wrong before the operations are completed, you will probably still have either the original or temporary file. text[0..-2] is a string comprised of all characters read except for the last one. You could alternatively do this:
File.write(out_fname, File.read(in_fname, File.stat(in_fname).size-1))
I have a program that is reading a text file, and owing to the vagaries of the file definition and the definitions of the objects the data has to be shovelled in to, I appear to have a need to move the read pointer of the file back up the file for a line, in a manner roughly analagous to the FORTRAN BACKSPACE statement.
Is there any method of doing this, either with native VB6 statements or with VB6 FileSystem objects?
I'm pretty sure VB6 provides a seek() function to do this.
Otherwise, if the file is relatively small you could read it all into memory and use the split() function to separate it into lines. These could then be accessed however you want. Obviously if the file is large this is not a good idea though.
The FSO only lets you read forwards.
There isn't a way to do this in VB6. What you could do is to either read the whole file, a line at a time, into an array and then iterate through the array as needed. Or if that caused memory issues, then create a data structure and use Input to read a line into an instance of the structure based upon the line number.
I have an XML file (actually a Visual C# project file) that I want to manipulate using a Ruby script. I want to read the XML into memory, do some work on them that includes changing some attributes and some text (fixing up some path references), and then write the XML file back out. This isn't so hard.
The hard part is, I want the file I write to look the same as the file I read in, except where I made changes. If the input file used double quotes, I want the output to use double quotes. If the input had a space before />, I want the output to do the same. Basically, I want the output to be the same as the input, except where I explicitly made changes (which, in my case, will only be to attribute values, or to the text content of an element).
I want minimal diffs because this project file is checked into version control -- and because the next time I make a change in Visual Studio, it's going to rewrite it in its preferred format anyway. I want to avoid checking in a bunch of meaningless diffs that will then be changed back again in the near future. I also want to avoid having to open the project in Visual Studio, make a change, and save, before I can commit my Ruby script's changes. I want my Ruby script to just make its changes, nothing more.
I originally just parsed the file with regexes, but ran into cases where I really needed an XML library because I needed to know more about child elements. So I switched to REXML. But it makes the following undesirable changes to my formatting:
It changes all the attributes from double quotes to single quotes.
It escapes all the apostrophes inside attribute values (changing them to ').
It removes the space before />.
It sorts each element's attributes alphabetically, rather than preserving the original order.
I'm working around this by doing a bunch of gsub calls on REXML's output, but is there a Ruby XML-manipulation library that's a better fit for "minimal diff" scenarios?
You can build your own SAX parser (using Nokogiri, for example, it's very easy and I recommend to use it) to parse your XML file, change some data in it, and flush the processed XML file with your own customized, built from scratch, XML generator. The bad news is, you have to build a tiny XML library and generator routine in this case, so it is not an ordinary task.
Another way: don't build the SAX parser, but write an XML generator. Parse XML with your favourite library, change what you need to change and generate anything you want. You just need to recursively walk through all nodes in your document and output them within your conventions.