C file input/output#FILE pointer

This library uses what are called streams to operate with physical devices such as keyboards, printers, terminals or with any other type of files supported by the system. Streams are an abstraction to interact with these in a uniform way. All streams have similar properties independent of the individual characteristics of the physical media they are associated with.{{Cite web |title=(stdio.h) - C++ Reference |url=http://www.cplusplus.com/reference/cstdio/ |access-date=July 25, 2021 |website=C++ |language=en-US}}

Most of the C file input/output functions are defined in {{mono|}} (or in the C++ header {{mono|cstdio}}, which contains the standard C functionality but in the {{mono|std}} namespace).

Constants defined in the {{mono|}} header include:

File:Stdstreams-notitle.svg

Variables defined in the {{mono|}} header include:

Data types defined in the {{mono|}} header include:

• {{mono|[https://en.cppreference.com/w/c/io FILE]}} – also known as a {{anchor|file handle}}file handle or a {{Visible anchor|FILE pointer}}, this is an opaque pointer containing the information about a file or text stream needed to perform input or output operations on it, including:
• platform-specific identifier of the associated I/O device, such as a file descriptor
• the buffer
• stream orientation indicator (unset, narrow, or wide)
• stream buffering state indicator (unbuffered, line buffered, fully buffered)
• I/O mode indicator (input stream, output stream, or update stream)
• binary/text mode indicator
• end-of-file indicator
• error indicator
• the current stream position and multibyte conversion state (an object of type mbstate_t)
• reentrant lock (required as of C11)
• {{mono|fpos_t}} – a non-array type capable of uniquely identifying the position of every byte in a file and every conversion state that can occur in all supported multibyte character encodings
• {{mono|size_t}} – an unsigned integer type which is the type of the result of the {{mono|sizeof}} operator.

The POSIX standard defines several extensions to {{mono|stdio}} in its Base Definitions, among which are a {{mono|readline}} function that allocates memory, the {{mono|fileno}} and {{mono|fdopen}} functions that establish the link between {{mono|FILE}} objects and file descriptors, and a group of functions for creating {{mono|FILE}} objects that refer to in-memory buffers.{{man|bd|stdio.h|SUS}}

The following C program opens a binary file called myfile, reads five bytes from it, and then closes the file.

1. include
2. include

int main(void) {

char buffer[5];

FILE* fp = fopen("myfile", "rb");

if (fp == NULL) {

perror("Failed to open file \"myfile\"");

return EXIT_FAILURE;

}

if (fread(buffer, 1, 5, fp) < 5) {

fclose(fp);

fputs("An error occurred while reading the file.\n", stderr);

return EXIT_FAILURE;

}

fclose(fp);

printf("The bytes read were: ");

for (int i = 0; i < 5; ++i) {

printf("%02X ", buffer[i]);

}

putchar('\n');

return EXIT_SUCCESS;

}

{{Redirect|Sfio|other uses of "SFIO"|SFIO (disambiguation)}}

Several alternatives to {{mono|stdio}} have been developed. Among these is the Input/output (C++) library, part of the ISO C++ standard. ISO C++ still requires the {{mono|stdio}} functionality.

Other alternatives include the Sfio{{Cite web |url=http://akpublic.research.att.com/sw/tools/sfio/ |title=Sfio: A Safe/Fast I/O Library |access-date=16 March 2021 |archive-date=11 February 2006 |archive-url=https://web.archive.org/web/20060211021834/http://akpublic.research.att.com/sw/tools/sfio/ |url-status=bot: unknown }} (A Safe/Fast I/O Library) library from AT&T Bell Laboratories. This library, introduced in 1991, aimed to avoid inconsistencies, unsafe practices and inefficiencies in the design of {{mono|stdio}}. Among its features is the possibility to insert callback functions into a stream to customize the handling of data read from or written to the stream.{{cite conference |title=SFIO: Safe/Fast String/File IO |first1=David G. |last1=Korn |author-link=David Korn (computer scientist) |first2=Kiem-Phong |last2=Vo |conference=Proc. Summer USENIX Conf. |year=1991 |citeseerx=10.1.1.51.6574}} It was released to the outside world in 1997, and the last release was 1 February 2005.{{cite conference |first1=Glenn S. |last1=Fowler |first2=David G. |last2=Korn |first3=Kiem-Phong |last3=Vo |title=Extended Formatting with Sfio |conference=Proc. Summer USENIX Conf. |year=2000}}

• printf format string
• scanf format string

{{Reflist}}

{{wikibooks|C Programming|C file input and output|C Programming/C Reference}}

• {{Commons category-inline}}

{{CProLang}}

{{DEFAULTSORT:C file input output}}

Category:C standard library

Category:Input/output

Category:Articles with example C code