Hello everyone!
I need to concatenate 3 files using C#. A header file, content, and a footer file, but I want to do this as cool as it can be done.
cool = really small code or really fast (non-assembly code).
+4
A:
Not sure what constitutes cool, but it seems cool these days to use LINQ for everything:
File.ReadAllText(a) + File.ReadAllText(b) + File.ReadAllText(c)
Not sure what constitutes cool, but it seems cool these days to use LINQ for everything:
string.Join("", Array.ConvertAll(new[] { "file1","file2", "file3" }, File.ReadAllText));
Jimmy
2009-01-14 19:21:26
disclaimer: will not work for large files. See Mehrdad Afshari's code for what to do then.
Jimmy
2009-01-14 19:23:12
This looks like it will need a lot of memory to hold all three files in memory as a string, let alone the intermediate string object resulting by adding the first two and the final string created by adding on the last.
Brian Ensink
2009-01-14 19:26:56
Jimmy you beat me to it with your own disclaimer! :)
Brian Ensink
2009-01-14 19:27:36
1) Concating strings are not good practise. You should use stringbuilder.2) This is not good solution for binary files.
TcKs
2009-01-14 19:40:43
@TcKs: 1) inline concatenation here is done by string.concat(a,b,c) in one operation, with lower overhead than stringbuilder 2) I assumed "header/content/footer" files were text.
Jimmy
2009-01-14 19:57:13
+7
A:
void CopyStream(Stream destination, Stream source) {
int count;
byte[] buffer = new byte[BUFFER_SIZE];
while( (count = source.Read(buffer, 0, buffer.Length)) > 0)
destination.Write(buffer, 0, count);
}
CopyStream(outputFileStream, fileStream1);
CopyStream(outputFileStream, fileStream2);
CopyStream(outputFileStream, fileStream3);
Mehrdad Afshari
2009-01-14 19:22:05
i don't find this so smart. What is a good BUFFER_SIZE? nobody knows. compared to File.ReadAllText(a) + File.ReadAllText(b) + File.ReadAllText(c), this looks like premature optimization to me.
nes1983
2009-01-14 19:50:58
Depends on the size of your files. You would not like to concatenate a few hundred megabytes using the ReadAllText method.
gimpf
2009-01-14 19:54:42
I agree. But in such cases, I would really leave such a task to the experts that wrote a library or, as would cross my thoughs, the cat program. I would certainly not read it chunkwise with some chunk-size a fair dice-roll gave me.
nes1983
2009-01-14 20:14:21
In fact, this is the traditional method to copy a stream. A good buffer size depends on the specific situation, but probably it has to be a multiple of block size at very least. Remember, file sizes are among the things that easily go beyond 32 bit integer max value ;)
Mehrdad Afshari
2009-01-14 22:56:28
Yea, I've seen this method. but is it smart to pretend low-level in a language like C#? to get this right, you have to consider context switches, library io buffers, etc. Buffer-copying is low-level stuff and should be done on the low level, if you REALLY need it, which isn't the usual case.
nes1983
2009-01-15 05:51:11
@Nico, I don't how you interpreted my statement. I meant, the amount of simplicity and smartness depends on the situation. In this special case (using files), the performance of loading the whole files can be extremely critical which cannot always be ignored just because you're coding in C#.
Mehrdad Afshari
2009-01-15 13:46:01
Most cases, Jimmy's way of doing it is fine. If you have large files and need speed, reading from the output of "cat file1 file2 file3" is probably going to be faster than having the buffer on the C# side.
nes1983
2009-01-15 14:33:32
It might be but it has some other problems. Creating the process, introducing platform dependence, reliance on a third party program and making stuff more complex. You have to make these trade-offs and the "right" solution depends on the specific scenario.
Mehrdad Afshari
2009-01-15 14:41:59
I was thinking all the time why you think it's that much "low-level". I thought it might worth mentioning that FileStreams are internally buffered, so the array here is not doing any actual file buffering to reduce low level syscalls. It's just reducing method calls and it's not that low level.
Mehrdad Afshari
2009-01-15 17:07:50
Yea, but this is kind of my point: using these buffers looks low-level and complicated, but actually it's above the library-buffer, which reads from the OS buffer, which reads from the disc buffer. if i want to use buffers, i do it low-level. if i want to attach files high-level, i do f1+f2+f3.
nes1983
2009-01-15 20:06:43
+1
A:
i don't know C# so well - can you call the shell from there? can you do something like
system("type file1 file2 file3 > out");
?
i believe that asymptotically, this ought to be very fast.
niko
nes1983
2009-01-14 19:28:39
+2
A:
Another way....how about letting the OS do it for you?:
ProcessStartInfo psi = new ProcessStartInfo("cmd.exe",
String.Format(@" /c copy {0} + {1} + {2} {3}",
file1, file2, file3, dest));
psi.UseShellExecute = false;
Process process = Process.Start(psi);
process.WaitForExit();
HTH
Kev
Kev
2009-01-14 19:47:21
+1
A:
You mean 3 text files?? Does the result need to be a file again?
How about something like:
string contents1 = File.ReadAllText(filename1);
string contents2 = File.ReadAllText(filename2);
string contents3 = File.ReadAllText(filename3);
File.WriteAllText(outputFileName, contents1 + contents2 + contents3);
Of course, with a StringBuilder and a bit of extra smarts, you could easily extend that to handle any number of input files :-)
Cheers, Marc
marc_s
2009-01-14 20:18:30