I want to copy some files from one folder to other folder and before copying or replacing the files I want to take backup from destination folder only those file which are I am trying to copy in to source file to destination file.
This is what I want to do but is this possible in pure C-language?.
First of all you should say on which platform you want to do that.
I'm not that familiar with Windows so what i'll be saying only applies to Linux (maybe it works on windows as well but I doubt it).
Have a look on man opendir and man readdir and those are the only things you need to do what you want (you obviously will also need to open/read/write and close but I imagine that you know that).
There's no native way in C to do that. You need platform-specific code. The simplest way to achieve that is to use the system() function
system("copy C:\\Windows\\notepad.exe D:\\"); // Windows
or
system("cp ~/myfile.txt ~/mycopiedfile.txt"); // *nix
But for better performance and/or more control over the result you need to call the corresponding APIs if available (like CopyFile() on Windows), or copy the file on your own by reading from source to a buffer with fread() then write to the destination with fwrite()
See Is there a POSIX function to copy a file?
Related
I have a set of configuration files (10 or more), and if user opens any of these file using any editor (e.g vim,vi,geany,qt,leafpad..). How would I come to know that which file is opened and if some writing process is done, then it is saved or not (using C code).
For the 1st part of your question, please refer e.g. to How to check if a file has been opened by another application in C++?
One way described there is to use a system tool like lsof and call this via a system() call.
For the 2nd part, about knowing whether a file has been modified, you will have to create a backup file to check against. Most editors already do that, but their naming scheme is different, so you might want to take care of that yourself. How to do that? Just automatically create a (hidden) file .mylogfile.txt if it does not exist by simply copying mylogfile.txt. If .mylogfile.txt exists, is having an older timestamp than mylogfile.txt, and differs in size and/or hash-value (using e.g. md5sum) your file was modified.
But before re-implementing this, take a look at How do I make my program watch for file modification in C++?
I'm writing a program in C that sends files across the network using sockets. This works fine for files - they are read into a buffer and then written onto the socket. They are picked up at the other end by reversing this process.
However, how can this apply to directories? I also want to copy directories, keeping the permissions the same (so I don't think mkdir will work). At the moment when I try to run this on a directory, it says the size is -1. How is a directory represented?
To be clear, for example, if I want my program to copy /tmp across the network, it will do this:
/tmp/1.txt - OK
/tmp/2.txt - OK
/tmp/dir/ - Skip
/tmp/dir/3.txt - Can't write to path
There are several possibilities. It would fit fairly will with what you have already to tar the directory to transfer, send the resulting archive across the network, and untar on the other side.
Alternatively, you can walk the directory tree recursively. For each directory you need transfer only the name and whichever attributes you want to preserve, but then you must list the directory contents (probably via readdir()) and transfer each member.
By the way, don't neglect to think about how you're going to handle links, both symbolic ones and hard ones. And if you want your program to be really robust then consider also what to do with special files such as device files and FIFOs.
I guess it is homework, otherwise why not use FTP, scp, rsync, unison etc.
To test if a file path is a plain file, a device, a directory, etc etc... use
stat(2)
To read a directory, use opendir(3) then loop on readdir(3) (then of course closedir). You don't need to know how a directory is represented.
You probably should be interested in nftw(3) to recursively traverse a file tree.
To make one directory, use mkdir(2)
You should read Advanced Linux Programming
BTW, this answer contains useful information too...
I'm trying to use a system call to display the contents of a directory. I've been pointed in the direction of vfs_readdir, but I have no clue of how to use it or what to pass to it to get the contents of a directory. All I want to do is be able to list files in a directory similar to how ls works. (I eventually intend to store this in some sort of buffer, but for now just being able to print the contents of a dir would be enough).
I think you probably have to open the directory using filp_open.
For the "flags" argument, you proably need to put some combination of the LOOKUP_ flags listed in include/linux/namei.h
You can see what build_open_flags does here: http://lxr.linux.no/#linux+v3.1.5/fs/open.c#L876 to provide flags to filp_open.
As far as I know, filp_open IS the correct way of opening a file in kernel-space. However, doing so is discouraged.
Provided you do so from the context of a "normal" thread belonging to a user process, I think you will be ok.
just had a general question about how to approach a certain problem I'm facing. I'm fairly new to C so bear with me here. Say I have a folder with 1000+ text files, the files are not named in any kind of numbered order, but they are alphabetical. For my problem I have files of stock data, each file is named after the company's respective ticker. I want to write a program that will open each file, read the data find the historical low and compare it to the current price and calculate the percent change, and then print it. Searching and calculating are not a problem, the problem is getting the program to go through and open each file. The only way I can see to attack this is to create a text file containing all of the ticker symbols, having the program read that into an array and then run a loop that first opens the first filename in the array, perform the calculations, print the output, close the file, then loop back around moving to the second element (the next ticker symbol) in the array. This would be fairly simple to set up (I think) but I'd really like to avoid typing out over a thousand file names into a text file. Is there a better way to approach this? Not really asking for code ( unless there is some amazing function in c that will do this for me ;) ), just some advice from more experienced C programmers.
Thanks :)
Edit: This is on Linux, sorry I forgot to metion that!
Under Linux/Unix (BSD, OS X, POSIX, etc.) you can use opendir / readdir to go through the directory structure. No need to generate static files that need to be updated, when the file system has the information you want. If you only want a sub-set of stocks at a given time, then using glob would be quicker, there is also scandir.
I don't know what Win32 (Windows / Platform SDK) functions are called, if you are developing using Visual C++ as your C compiler. Searching MSDN Library should help you.
Assuming you're running on linux...
ls /path/to/text/files > names.txt
is exactly what you want.
opendir(); on linux.
http://linux.die.net/man/3/opendir
Exemple :
http://snippets.dzone.com/posts/show/5734
In pseudo code it would look like this, I cannot define the code as I'm not 100% sure if this is the correct approach...
for each directory entry
scan the filename
extract the ticker name from the filename
open the file
read the data
create a record consisting of the filename, data.....
close the file
add the record to a list/array...
> sort the list/array into alphabetical order based on
the ticker name in the filename...
You could vary it slightly if you wish, scan the filenames in the directory entries and sort them first by building a record with the filenames first, then go back to the start of the list/array and open each one individually reading the data and putting it into the record then....
Hope this helps,
best regards,
Tom.
There are no functions in standard C that have any notion of a "directory". You will need to use some kind of platform-specific function to do this. For some examples, take a look at this post from Cprogrammnig.com.
Personally, I prefer using the opendir()/readdir() approach as shown in the second example. It works natively under Linux and also on Windows if you are using Cygwin.
Approach 1) I would just have a specific directory in which I have ONLY these files containing the ticker data and nothing else. I would then use the C readdir API to list all files in the directory and iterate over each one performing the data processing that you require. Which ticker the file applies to is determined only by the filename.
Pros: Easy to code
Cons: It really depends where the files are stored and where they come from.
Approach 2) Change the file format so the ticker files start with a magic code identifying that this is a ticker file, and a string containing the name. As before use readdir to iterate through all files in the folder and open each file, ensure that the magic number is set and read the ticker name from the file, and process the data as before
Pros: More flexible than before. Filename needn't reflect name of ticker
Cons: Harder to code, file format may be fixed.
but I'd really like to avoid typing out over a thousand file names into a text file. Is there a better way to approach this?
I have solved the exact same problem a while back, albeit for personal uses :)
What I did was to use the OS shell commands to generate a list of those files and redirected the output to a text file and had my program run through them.
On UNIX, there's the handy glob function:
glob_t results;
memset(&results, 0, sizeof(results));
glob("*.txt", 0, NULL, &results);
for (i = 0; i < results.gl_pathc; i++)
printf("%s\n", results.gl_pathv[i]);
globfree(&results);
On Linux or a related system, you could use the fts library. It's designed for traversing file hierarchies: man fts,
or even something as simple as readdir
If on Windows, you can use their Directory Management API's. More specifically, the FindFirstFile function, used with wildcards, in conjunction with FindNextFile
I want to make a small program which use local namespace socket and I will need to use temporary file name as address of the socket.
So how to generate random file name under Linux?
+ I'm using the C programming language under Debian Linux.
+ Acoording to the GNU C Library Reference,tmpname is not safe.But the safe ones tmpfile and mkstemp create and open the generated file.Is there any safe and non-create-open to this.In other words, the function should forbidden any other request to create the generated file name under specific directory.
thanks.
If you're doing this in C, use mkdtemp to create a directory, and put your socket inside this directory.
Other functions such as tmpnam or mktemp are insecure; since they don't create and open the temp file for you, it's easy to be vulnerable to following a pre-existing symlink (placed by an attacker who guessed your temp filename) to some important file (like /etc/passwd), overwriting it.
Note that there's no way to 'lock' a path - all you can do is create something there. If you need to put a socket there eventually, using a directory as a placeholder is your best bet.
There is mktemp program which is available as part of GNU coreutils. See it's manpage for details.
Typical usage is as simple as this:
TEMPDIR=$(mktemp -d)
echo $TEMPDIR
touch $TEMPDIR/yourfile.txt
(As noted in other answer it is only safe to create a directory.)
You didn't specify the language you are using, but assuming it is a C/C++ dialect (or some other language with access to the C runtime library), you could use the tmpnam function.
There are some issues with tmpnam, the most serious of which is probably that the temporary file name you get back isn't actually "locked" until you use it to create a file, so theoretically some other process could create the file out from under you. You also have to make absolutely sure the buffer you pass tmpnam has enough space to hold the longest path your OS can support.
These days it is recommended that you call tmpfile instead. This will create the file for you in one (hopefully atomic) operation, and give you back a file handle. Another nice benefit is that the file is deleted for you automatically when you close it. No muss, no fuss.
Play with /dev/random.
A quick search on google gave me this hit:
< /dev/urandom tr -dc A-Za-z0-9 | head -c8
If you would like to do the same in C,
just open /dev/random and convert it into a string (ignore non valid chars).