The operations that are allowed on the stream and how these are performed are defined by the mode parameter.
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.
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. 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.Oct 22, · So if you desire to write a file that is to be used specifically in Windows, you can do your own "new line" rather than using the servers.
Use PUT rather than PUT_LINE and just append the two characters Windows uses for "new line". io_read Reads from the file. io_write Write in the file, or create the file if it does not exist. Erases all existing contents.
io_readwrite Reads the file or creates it if it doesn't already exist. io_append Appends (adds) to file, write-only. fopen, fopen_s. From r-bridal.com Create a file for read/write destroy contents create new "a+" append extended Open a file for read/write write to end create new File access mode flag "b" can optionally be specified to open a file in binary mode.
How to properly append lines to already existing file. Ask Question. "write line by line to a file" would (to me at least) Check the man page of fopen() for a or append mode.
Case 2 (Opening / Closing once, writing all the values at a stretch) you need to put the fprintf(). Basic PHP File Handling — Create, Open, Read, Write, Append, Close, and Delete Building Resilient Systems on AWS: Learn how to design and implement a resilient, highly available, fault-tolerant infrastructure on AWS.
freopen, freopen_s. Same as (1), except that mode is treated as in fopen_s and that the pointer to the file stream is written to newstreamptr and the following errors are detected at runtime and call the currently installed constraint handler function: append extended Open a file for read/write write to end.