C file input/output: Difference between revisions

Revision as of 11:54, 30 January 2005

Revision as of 02:49, 6 April 2005

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{{wrongtitle|title="fopen"}}

In [[computer programming]], the <code>'''fopen'''</code>, with related functions <code>'''fdopen'''</code> and '''<code>freopen</code>''',function is one of the basic functions in the [[C programming language]]. and also exists in various other computer languagesIt suchreturns asan [[PHPI/O]]. They return a [[stream]] attached to the specified [[computer file|file]] or other device from which reading and writing can be done. Because itthe functionality is so popularuseful, many script languages derived from C tendprovide tofunctions provideof the same functionname, with the same or similar functionalityfunction: for example, [[PHP]]. It<code>fopen</code> is considered higher-level than the <code>[[open]]</code> [[system call]] of UNIX operating systems. The related C library function '''<code>freopen</code>''' performs the same operation after first closing any open stream associated with its parameter.

They are defined as.

They are defined as.

:<code>FILE * fopen(const char *path, const char *mode);</code>

:<code>FILE * fdopen(int fildes, const char *mode);</code>

:<code>FILE * freopen(const char *path, const char *mode, FILE * restrict stream);</code>

The '''<code>fdopen</code>''' function is not standard in C89 or C99, but is an extension used in [[POSIX]] environments and imitated elsewhere.

The '''mode''' parameter is a string that begins with one of the following sequences:

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a+b or ab+ Append: open or create binary file for update, writing at end-of-file

The C standard gives two kinds of files: &mdash; text files and binary files, &mdash; although operating systems may or may not distinguish between the two. A ''text file'' is a file consisting of text arranged in lines with some sort of distinguishing end-of-line character or sequence (in [[Unix]], a bare linefeed character; in the [[Apple Macintosh|Macintosh]] OS, a bare carriage return; on [[DOS]] and [[Microsoft Windows]], a carriage return followed by a linefeed). When bytes are read in from a text file, an end-of-line sequence is usually mapped to a linefeed for ease in processing. When a text file is written to, a bare linefeed is mapped to the OS-specific end-of-line character sequence before writing. A ''binary file'' is a file where bytes are read in "raw"," and delivered "raw"," without any kind of mapping.

A convenient way to find the length of a file in C is:

<pre><nowiki>

FILE *f = fopen("filename", "rb");

fseek(f, 0, SEEK_END);

length = tell(f);

rewind(f);

</nowiki></pre>

[[Category:C standard library]]