Introductory C, Second Edition: Pointers, Functions, and Files: Pointers, Functions and Files

General C++ Coding Standard at the NFRA
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In contrast, you can also use 'b' to force binary mode, which will not translate your data. To use these flags, specify either 'b' or 't' as the last character of the mode parameter.

Motivation and Benefits

The default translation mode depends on the SAPI and version of PHP that you are using, so you are encouraged to always specify the appropriate flag for portability reasons. You should use the 'b' in all other cases. Note : For portability, it is strongly recommended that you always use the 'b' flag when opening files with fopen.

Note : Again, for portability, it is also strongly recommended that you re-write code that uses or relies upon the 't' mode so that it uses the correct line endings and 'b' mode instead. Note : Context support was added with PHP 5. For a description of contexts , refer to Streams. Version Description 7. Example 1 fopen examples. Note : When safe mode is enabled, PHP checks whether the directory in which the script is operating has the same UID owner as the script that is being executed. Note : If you are experiencing problems with reading and writing to files and you're using the server module version of PHP, remember to make sure that the files and directories you're using are accessible to the server process.

Note : This function may also succeed when filename is a directory. Edit Report a Bug.

NAG Library

Changelog Version Description 7. Note - using fopen in 'w' mode will NOT update the modification time filemtime of a file like you may expect.

You may want to issue a touch after writing and closing the file which update its modification time. This may become critical in a caching situation, if you intend to keep your hair. With php 5. It looks like the second one is needed so the server won't interpret the path as relative to blossom's home on townsville.

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Note that whether you may open directories is operating system dependent. On UNIX, you may happily read the directory format for the native filesystem. This functions check recursive permissions and recursive existence parent folders, before creating a folder. Supports "Location:"-redirections. Works with SSL-secured hosts. The manual doesn't make it crystal-clear that fopen in write mode will not create a new file in the Include Path, even if there is only one directory in the Include Path.

The Include Path is for searching, which means for reading files only. Also avoid these names followed immediately by an extension; for example, NUL. For more information, see Namespaces" it is a windows limitation.

So if you have the same problem, goto your php. Now adding a line also means deleting the very first one. The second user would then rewrite an incomplete file and add its line to it, meaning: you just got yourself some data loss! So I came up with another solution for the file-interference-problem: 1. The temp-file gets a random filename, ensuring no other process is able to interfere with this particular temp-file.

But if filemtime has been changed while our PHP-process wanted to change its file, the temp-file will just be deleted and our new PHP-fileclose-function will return a FALSE, enabling whatever called that function to do it again ie. To ensure file-integrity, your changes were rejected. If you are getting message "Warning: fopen : URL file-access is disabled in the server configuration", you can use function below to get the content from a local or remote file.

Which contains an array of the response header. Used iconv to convert it to UTF-8 and it resolved the issue. PHP will open a directory if a path with no file name is supplied. This just bit me. I was not checking the filename part of a concatenated string. I tried append mode and it errors out so does not seem to be dangerous. This is with FreeBSD 4. Behaves the same on 4. I was working on a consol script for win32 and noticed a few things about it.

On win32 it appears that you can't re-open the input stream for reading, but rather you have to open it once, and read from there on. Also, i don't know if this is a bug or what but it appears that fgets reads until the new line anyway. The number of characters returned is ok, but it will not halt reading and return to the script.

Part I: Introductory Material

C differs from most programming languages in its use of pointers, functions, and files. For those learning C, pointers are the greatest source of confusion. Introductory C, Second Edition: Pointers, Functions, and Files 2nd edition by Petersen, Richard L. () Paperback on *FREE* shipping on.

I don't know of a work around for this right now, but i'll keep working on it. This is some code to work around the close and re-open of stdin. I couldn't for the life of me get a certain php script working when i moved my server to a new Fedora 4 installation. The problem was that fopen was failing when trying to access a file as a URL through apache -- even though it worked fine when run from the shell and even though the file was readily readable from any browser.

This is an addendum to ibetyouare at home dot com's note about Apache directory permissions.

  • Pocket Guide for Presenters: Express yourself with confidence.
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  • Life Lessons from the Monk Who Sold His Ferrari.
  • 7.8 — Function Pointers.
  • References.

In practice, I'd never write such a for loop in a program. Instead, I'd use the built-in strcpy function. There are several library functions built into C for working with strings. Their prototypes are in the string. Following are three. C has no support for strings of indefinite length. You can move the NUL character forward in the array to make it shorter, but you can't move it past the end of an array.

The function is to split the string buf into separate words, placing pointers to successive words into argv and returning the number of words found. We'd place this into an array of characters and pass this string as buf into the function. The function's job is to place pointers into argv to the individual words. The function accomplishes this by replacing spaces in the sentence with NUL characters and pointing the array entries referenced by argv into the sentence's array.

It uses the isspace function for identifying space characters; this function's prototype is in the ctype. Although C doesn't have the notion of class as in object-oriented languages, it does have the structure , which allows you to define a new data type representing a conglomeration of data. The primary distinction between a class and a structure is that a class can have both variables and methods, while a structure can have only variables.

In C, struct is part of the type name for every structure defined. But we're talking about C now. So you can write the following which does nothing interesting except illustrate a C structure's use. Notice how a structure is automatically created at the beginning of the function, with the variable declaration, and it automatically goes away at the function's end.

You can easily make an array of structures, talk about pointers to structures, or place a structure within another structure. When you pass a structure as a parameter, you should pass a pointer to the structure, not the structure itself. The reason is that structures tend to contain lots of data, and copying all of the fields into the parameter variable is inefficient. Thus, the following definition is equivalent. Sometimes you want to allocate memory in the course of running a program. To do this, you can use the malloc function included in the C library.

The malloc function takes a single integer, which represents how many bytes the function should allocate, and it returns the memory address of the first byte of memory allocated. In computing how many bytes to allocate, the sizeof operator is useful: Given a type, the sizeof operator computes how many bytes a value of that type requires.

In the malloc line, we've opted to allocate enough memory to hold n integers. When you allocate memory in C, you should deallocate it later to free the space. To accomplish this, you can use the free function, which takes a pointer as a parameter and marks the memory to which it points as available. After you deallocate memory, you should not use it again. Neither should you deallocate the memory a second time.

Learn C on the Mac: For OS X and iOS, Second Edition

Avoiding both of these issues can be pretty painful. But it should be deallocated. If the program ends, all memory used by the program will be deallocated automatically. But, if the program continues for a long period and unused memory is never deallocated, then the program's memory requirements will grow steadily, leading to strange problems later once memory runs out. This is called a memory leak.

numpy.i: a SWIG Interface File for NumPy — NumPy v Manual

Python avoids the issue of memory deallocation entirely by letting the computer automatically figure out when memory becomes available. This automatic process, called garbage collection , is complex, and efficient techniques for it were unknown at the time of C's development, so C opts to let the programmer control memory deallocation. For Python's designers, faster computers and more efficient collection techniques, coupled with a different target audience, tilted the scale toward automatic garbage collection instead.

Techniques for garbage collection are interesting but unfortunately beyond the scope of what we're studying here. The more intuitive way of writing this function is to have a cur variable stepping through the list, but this necessitates tracking the previous node, since that node's pointer to its successor will change once cur points to the node to remove.

It's not really a better implementation, but it does illustrate an interesting use of pointers. It would be tempting to write the listRemove function's if statement as follows instead. This change avoids the out variable altogether, and so we could also delete out 's declaration. Thus, this change results in a wrong program. This concludes our introduction to C programming.

Fseek() function concept in file

While we have of course omitted discussion of several features of C, you should now be well on your way to understanding most C code that you might encounter. Based on a work at www.