C open file for writing append

What is FileStream Class? Methods and Properties of FileStream Class.

C open file for writing append

If a file by that name already exists, it will be overwritten. When a file is opened for update, both input and output can be done on the resulting stream; however, output cannot be directly followed by input without an intervening fseek or rewind input cannot be directly followed by output without an intervening fseek, rewind, or an input that encounters end-of-file Return Value: On successful completion fopen returns a pointer to the newly opened stream.

In the event of error it returns NULL. I've found, in practice, that this doesn't work. The best way to open an existing file for appending and to create a file that doesn't exist is to make two separate calls to fopen. The first call tries to append to the file. If that fails when fopen returns 0then try opening the file using the "w" mode.

Create a file or open it for appending. This works but it has one little problem that you'll only notice at runtime.

c open file for writing append

In my test program, logit was called around times and the program took about 12 seconds longer to run.

That's okay if you only need to run the program like that a few times but I needed to run this program hundreds of times in a batch file. To solve this problem, I changed log to be a static variable. The code checks if log has been opened -- if not, the file is opened and log is initialized to the file's handle.

Since the file is open throughout the program's execution, I don't need to close it anymore so I've commented-out the fclose log call at the bottom of logit. Listing 2 shows the final logit function. This one has almost no execution time overhead. A static solution that runs faster.

As with most solutions, there is a downside. Because fopen usually buffers the output, If the program were to crash, the log file would be incomplete and could mislead you about what the program was doing when it crashed.

If having an up-to-date log file is important, add an fflush call to the parts of the logit function that involve important log messages. Of course, that will incur an execution-time cost, but at least the log file will be accurate.

c open file for writing append

Despite the documentation, fopen does not create files that don't exist when using any of the append modes. The best solution is to make two fopen calls: Because of the overhead involved in opening and closing a file, it's much better to open the file one time and keep it open for the rest of the program than it is to only have the file open when it's being written to.

If an accurate and up-to-date log file is mandatory, use fflush to guarantee that the output buffer is flushed before leaving any logging functions. This article was written by Curtis Krauskopf email at. Copyright The Database Managers, Inc.Text Files in C A file is for storing permanent data.

C provides file operations in stdio.h.A file is viewed as a stream of characters. Files must be opened before being accessed, and characters can be read one at a time, in order, from the file. To append a text or log file in C#, We writes the code for this and code is given below.

On the append file access modes, data is written to the end of the file regardless of the current position of the file position indicator. File access mode flag "x" can optionally be appended to . File I/O in C programming with examples: Learn how to create, open, read, write and close a file in C programming language with examples..

Mode “a+”: Same as mode “a”; you can read and append the data in the file, however content modification is not allowed in this mode. 2. Reading a File. A tutorial covering file I/O in C, including how to work with binary files.

Starting out a - open for appending (file need not exist) r+ - open for reading and writing, start at beginning w+ - open for reading and writing (overwrite file) a+ - open for reading and writing (append if file exists). Append; open for writing at end-of-file or create for writing if the file does not exist.

r+: Open an existing file for update (reading and writing). w+: Create a new file for update (reading and writing).

If a file by that name already exists, it will be overwritten.

fopen - C++ Reference