I know that there's no shortage of libraries out there for parsing INI files, but I just wanted one that could read in all of the section, key, value entries when my program starts and write them out before my program quits, so I thought that I'd write my own.
I'm not sure how you got here, or if you know what an INI file is. Anything else you'd do depends at least in some way on the specific environment your program runs in. Unfortunately said dance also has its problems as described in the articles you've linked. I guess you could always read everything out of the file until EOF and keep track along the way - with fread for example. The footnote appears in text dealing with wide-oriented streams , which are streams that the first operation that is performed on them is an operation on wide-characters.
This undefined behaviour stems from the combination of two paragraphs. Apparently this exists to allow binary files can have coarse size granularity, i. However, the C standard provides no way to distinguish between such cases, so you're stuck with system-dependent calls if you want to consider that. The underlying issue is that the "size" of a file in bytes is not always the same as the length of the data in the file and that, in some circumstances, the length of the data is not available.
A POSIX example is what happens when you write data to a device; the operating system only knows the size of the device. When the ANSI-C committee was sitting at the end of the 's a number of operating systems the members remembered simply did not store the length of the data in a file; rather they stored the disk blocks of the file and assumed that something in the data terminated it. The 'text' stream represents this.
Opening a 'binary' stream on those files shows not only the magic terminator byte, but also any bytes beyond it that were never written but happen to be in the same disk block. Consequently the C standard was written so that it is valid to use the fseek trick; the result is a conformant program, but the result may not be what you expect. Neither is it 'invalid'. Rather you get a number you can't completely rely on or, maybe, depending on the parameters to fseek, -1 and an errno.
In practice if the trick succeeds you get a number that includes at least all the data, and this is probably what you want, and if the trick fails it is almost certainly someone else's fault. But raw method is only by fread and fseek only: How can I get a file's size in C?
You can't always avoid writing platform-specific code, especially when you have to deal with things that are a function of the platform. I'd create my own generic wrapper around it, so as to not pollute application logic with platform-specific details and make the code easier to port.
It correctly identifies that a certain usage of C functions has behavior which is not defined by ISO C. But then, to avoid this undefined behavior, the article proposes a solution: replace that usage with platform-specific functions. Unfortunately, the use of platform-specific functions is also undefined according to ISO C.
Therefore, the advice does not solve the problem of undefined behavior. The quote in my copy of the standard confirms that the alleged behavior is indeed undefined:. But undefined behavior does not mean "bad behavior"; it is simply behavior for which the ISO C standard gives no definition.
Not all undefined behaviors are the same. Some undefined behaviors are areas in the language where meaningful extensions can be provided. The platform fills the gap by defining a behavior. Providing a separate function like lseek is also an extension in place of undefined behavior the undefined behavior of calling a function which is not in ISO C and not defined in the C program. It is fine to use that, if available. So, if fseek does provide the desired behavior on the given platform, then nothing has to be done to the program; it is a waste of effort to change it to use that platform's special function.
On the other hand, if fseek does not provide the behavior, then likely nothing does, anyway. The fgetc returns an int. What this actually means is that when it reads a normal character in the file, it will return a value suitable for storing in an unsigned char basically, a number in the range 0 to On the other hand, when you're at the very end of the file, you can't get a character value--in this case, fgetc will return "EOF", which is a constnat that indicates that you've reached the end of the file.
The fputc function allows you to write a character at a time--you might find this useful if you wanted to copy a file character by character. It looks like this:. Note that the first argument should be in the range of an unsigned char so that it is a valid character.
This chapter will take you through the important calls for file management. You can use the fopen function to create a new file or to open an existing file. This call will initialize an object of the type FILE , which contains all the information necessary to control the stream. Opens a text file for writing. If it does not exist, then a new file is created.
Here your program will start writing content from the beginning of the file. Opens a text file for writing in appending mode.
Here your program will start appending content in the existing file content. Opens a text file for both reading and writing. It first truncates the file to zero length if it exists, otherwise creates a file if it does not exist.
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