I'm trying to open an existent file save a bytes in the start of it to later read them.
How can I do that? Because the "&" operand isn't working fo this type of data.
I'm using Encoding.UTF8.GetBytes("text") to convert info to bytes and then add them.
Help Please.
You cannot add to or remove from the beginning of a file. It just doesn’t work. Instead, you need to read the whole file, and then write a new file with the modified data. (You can, however, replace individual bytes or chunks of bytes in a file without needing to touch the whole file.)
Secondly,
I'm using Encoding.UTF8.GetBytes("text") to convert info to bytes and then add them.
You’re doing something wrong. Apparently you’ve read text data from the file and are now trying to convert it to bytes. This is the wrong way of doing it. Do not read text from the file, read the bytes directly (e.g. via My.Computer.FileSystem.ReadAllBytes). Raw byte data and text (i.e. String) are two fundamentally different concepts, do not confuse them. Do not convert needlessly to and fro.
Related
Please note that I'm not asking how to append texts at the end of the file. I'm asking how to prepend texts to the beginning of file.
let handle = try FileHandle(forWritingTo: someFile)
//handle.seekToEndOfFile() // This is for appending
handle.seek(toFileOffset: 0) // Me trying to seek to the beginning of file
handle.write(content)
handle.closeFile()
It seems like my content is being written at the beginning of the file, but it just replaces the existing consent as well... Thanks!
One reasonable solution is to write the new content to a temporary file, then append the existing contents to the end of the temporary file. Then move the temporary file over the old file.
When you seek to a point in an existing file and then perform a write, the existing contents are overwritten from that point. This is why your current approach fails.
In general, most file systems don't have built-in support for prepending data to files. Likewise, most file I/O APIs don't either.
In order to prepend data, you first have to shift all of the existing data further along the file to make room for the new data at the beginning. You typically do this by starting near the end, reading a chunk of data, writing that data to the original position plus the length of data you hope to eventually prepend, and then repeating with the next chunk closer to the beginning of the file. In this way, you gradually shift everything down. Only after you've done all of that can you safely write the new data at the beginning of the file safely.
Frankly, if there's any way to avoid this, you should try to. The performance is likely to be terrible if the file is large and/or you're doing it frequently.
I have function which stores data in gzcompressed files, like
function savedata($fileName,&$data){
file_put_contents($filename,gzcompress($data));
}
I want to optimize and don't save if the data is same as in already stored gzcompressed file.
I can open the whole file, uncompress it and compare with the $data, but I think there should be some other way.Probably gz-d data has some crc or something like that, so I can just compress the data, fetch the crc from it and compare it to the crc in already existing file or something like that.
So I just want to omtimize checking the file and $data for changes to make it quicker.
gzcompress() in PHP compresses to the zlib format, not the gzip format.
Each zlib stream ends with a four-byte check value, though not a CRC. You can compare those to see if two streams are different. However if the two check values are the same, you cannot conclude that the streams are the same.
So I have a file that I need to have in either binary or hex format. Everything that I've been able to find basically says to store the text in a string and convert it to binary or hex from there, but I cant do it this way. The file was written using its own private character set that uses null and system hex codes, so notepad doesn't know what to do with these characters and replaces it with wrong characters and spaces. This distorts the information so it wont be correct if I try to convert it to binary/hex.
I really just need to have the binary/hex information stored in a string or text box so I can work with it. I don't really need it to be saved as a file.
Never mind, I finally figured it out. I used a file stream to read the data byte by byte. I didn't understand how to convert this as the first byte data in the array was showing as 80 when i knew the binary data should've been "1010000" (i didn't realize at that time that 80 was the decimal format).
Anyways I used the bitconverter.tostring and it put everything together and converted it to hexadecimal format. So i'm all good now.
I am looking for ways to read in a PDF file with SAS. Apparently this is not basic functionality and there is very little to be found on the internet. (Let alone that google is not easy with PDF in you search giving you also links to PDF documents that go about other things.)
The only things that can be found, are people looking for ways to import data into datasets from a PDF. For me, that is not even necesarry. I would like to be able to read the contents of the PDF file in one big character variable. If possible, it would even be better to be able to read in the file's binary data.
Is this possible with SAS and how? (I got it to work in Access VBA, but can't find any similar ways in SAS.)
(In the end, the purpose is to convert this to base64 and put that base64-string into an XML document.)
You probably will not be able to read the entire file into one character variable since the maximum size of a character variable is around 33 KB. A simple way to read in one line at a time, though, is something like the following:
%let pdfFileName = Test.pdf;
%let lineSize = 2000;
data base;
format text_line $&lineSize..;
infile "&pdfFileName" lrecl=&lineSize;
input text_line $;
run;
This requires that you have a general idea of the maximum record length ahead of time, but you could write additional code to determine the maximum record size prior to reading in the file. In this example each line of text is read into one character variable named "text_line." From there, you could use a RETAIN statement or double trailers (##) in the INPUT line to process multiple lines at a time. The SAS web-site has plenty of documentation on how to read and process text from various types of input files.
I have to read a file which in .dat format and separate data based on 2 first consecutive zero byte comes. first half is json data and other half is binary data.
How should I go about it?
I tried using NSData dataWithContentsOfFile method and read it and then convert it in byte array and compare bytes. Somehow, its not working.
You can use the same kind of procedure that you would use to read a file by lines. Here and here are earlier answers on SO regarding reading a file line-by-line. Just change \n to the byte sequence that is applicable.