io

问题 I have a file of 250 line. I wanted to insert some text after line 128. I only found that I can append a text at the end of file like try { PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("outfilename", true))); out.println("the text"); out.close(); } catch (IOException e) { //oh noes! } That is found on this post How to append text to an existing file in Java But with no mention to the line number or sth. 回答1: There's no way to insert text in the middle of a file because

问题 I am starting a small project for a key-value store, in C++. I am wondering how C++ std streams compare to mmap in terms of scalability and performance. How does using ifstream::seekg on a file that wouldn't fit in RAM compare to using mmap/lseek? 回答1: Ultimately, any Linux user-land application is using syscalls(2), including the C++ I/O library. With great care , mmap and madvise (or lseek + read & posix_fadvise ) could be more efficient that C++ streams (which are using read and other

问题 I have some code where I am serializing one of my classes that contains a DecimalFormat number. This worked up until 2.3.4. How can I resolve? ERROR/AndroidRuntime(684): java.lang.IllegalArgumentException: no char field 'exponential' Here is the class that I am serializing: public class Quote implements Serializable { private static final long serialVersionUID = 1L; private String symbol; private String name; private String change; private String percentChange; private String open; private

问题 I'm writing a program where I have to accept commands from the user like a shell where the user can set values for environment variables. The problem I'm having is if the user types set var var-value I need to know the user typed a space instead of just set and pressed enter which is a different command. How can I determine if the user pressed space or enter using scanf() ? 回答1: You'll know the user pressed enter because scanf() won't return until the user does so. If you're trying to read

问题 I'm writing a program where I have to accept commands from the user like a shell where the user can set values for environment variables. The problem I'm having is if the user types set var var-value I need to know the user typed a space instead of just set and pressed enter which is a different command. How can I determine if the user pressed space or enter using scanf() ? 回答1: You'll know the user pressed enter because scanf() won't return until the user does so. If you're trying to read

问题 I am observing a "Bad address" OSError when reading from a file handle created using the with syntax in Python 3. The file in question is 39G, but I should have enough RAM available to read the whole file. The error message leads me to believe I am hitting some kind of OS restriction; I am running CentOS 6.9. Can anyone help me understand what might be causing this behavior? The file is perfectly readable outside of python, e.g. in bash with head or vim . Simplified code sample producing the

问题 I've noticed that StringWriter uses internally a StringBuffer. But if you don't need that synchronisation overhead is there an equivalent to StringWriter that uses a StringBuilder inside? 回答1: If you happen to use Apache Commons IO, then you can re-use StringBuilderWriter which is described as follows: Writer implementation that outputs to a StringBuilder. NOTE: This implementation, as an alternative to java.io.StringWriter, provides an un-synchronized (i.e. for use in a single thread)

问题 I need to understand the difference between these two classes and how they work with each other. I understand that FileReader reads characters from a file one character at a time and the BufferedReader reads a large chunk of data and stores it in a buffer and thus makes it faster. In order to use a BufferedReader, i have to provide it a FileReader. How does the BufferedReader class use the FileReader if it reads the file differently? Does it mean that BufferedReader uses FileReader and

问题 Some background on why I'm asking this. I asked this question a few hours ago When a goroutine blocks on I/O how does the scheduler identify that it has stopped blocking? which had the answer All I/O must be done through syscalls, and the way syscalls are implemented in Go, they are always called through code that is controlled by the runtime. This means that when you call a syscall, instead of just calling it directly (thus giving up control of the thread to the kernel), the runtime is

问题 Overview of My Situation: My task is to read strings from a file, and re-format them to a more useful format. After reformatting the input, I have to write it to a output file. Here is an Example of what has to be done. Example of File Line : ANO=2010;CPF=17834368168;YEARS=2010;2009;2008;2007;2006 <?xml version='1.0' encoding='ISO-8859-1'?><QUERY><RESTITUICAO><CPF>17834368168</CPF><ANO>2010</ANO><SITUACAODECLARACAO>Sua declaração não consta na base de dados da Receita Federal<