The I/O functionality of C is fairly low-level by modern standards; C abstracts all file operations into operations on streams of bytes, which may be "input streams" or "output streams". Unlike some earlier programming languages, C has no direct support for random-access data files; to read from a record in the middle of a file, the programmer must create a stream, seek to the middle of the file, and then read bytes in sequence from the stream.
The stream model of file I/O was popularized by Unix, which was developed concurrently with the C programming language itself. The vast majority of modern operating systems have inherited streams from Unix, and many languages in the C programming language family have inherited C's file I/O interface with few if any changes (for example, PHP).
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.[4]
Functionsedit
Most of the C file input/output functions are defined in <stdio.h> (or in the C++ header cstdio, which contains the standard C functionality but in the stdnamespace).
Byte character
Wide character
Description
File access
fopen
Opens a file (with a non-Unicode filename on Windows and possible UTF-8 filename on Linux)
freopen
Opens a different file with an existing stream
fflush
Synchronizes an output stream with the actual file
fclose
Closes a file
setbuf
Sets the buffer for a file stream
setvbuf
Sets the buffer and its size for a file stream
fwide
Switches a file stream between wide-character I/O and narrow-character I/O
Direct input/output
fread
Reads from a file
fwrite
Writes to a file
Unformatted input/output
fgetc getc
fgetwc getwc
Reads a byte/wchar_t from a file stream
fgets
fgetws
Reads a byte/wchar_t line from a file stream
fputc putc
fputwc putwc
Writes a byte/wchar_t to a file stream
fputs
fputws
Writes a byte/wchar_t string to a file stream
getchar
getwchar
Reads a byte/wchar_t from stdin
gets
—
Reads a byte string from stdin until a newline or end of file is encountered (deprecated in C99, removed from C11)
putchar
putwchar
Writes a byte/wchar_t to stdout
puts
—
Writes a byte string to stdout
ungetc
ungetwc
Puts a byte/wchar_t back into a file stream
Formatted input/output
scanf fscanf sscanf
wscanf fwscanf swscanf
Reads formatted byte/wchar_t input from stdin, a file stream or a buffer
vscanf vfscanf vsscanf
vwscanf vfwscanf vswscanf
Reads formatted input byte/wchar_t from stdin, a file stream or a buffer using variable argument list
printf fprintf sprintf snprintf
wprintf fwprintf swprintf
Prints formatted byte/wchar_t output to stdout, a file stream or a buffer
vprintf vfprintf vsprintf vsnprintf
vwprintf vfwprintf vswprintf
Prints formatted byte/wchar_t output to stdout, a file stream, or a buffer using variable argument list
A negative integer of type int used to indicate end-of-file conditions
BUFSIZ
An integer which is the size of the buffer used by the setbuf() function
FILENAME_MAX
The size of a char array which is large enough to store the name of any file that can be opened
FOPEN_MAX
The number of files that may be open simultaneously; will be at least eight
_IOFBF
An abbreviation for "input/output fully buffered"; it is an integer which may be passed to the setvbuf() function to request block buffered input and output for an open stream
_IOLBF
An abbreviation for "input/output line buffered"; it is an integer which may be passed to the setvbuf() function to request line buffered input and output for an open stream
_IONBF
An abbreviation for "input/output not buffered"; it is an integer which may be passed to the setvbuf() function to request unbuffered input and output for an open stream
L_tmpnam
The size of a char array which is large enough to store a temporary filename generated by the tmpnam() function
NULL
A macro expanding to the null pointer constant; that is, a constant representing a pointer value which is guaranteed not to be a valid address of an object in memory
SEEK_CUR
An integer which may be passed to the fseek() function to request positioning relative to the current file position
SEEK_END
An integer which may be passed to the fseek() function to request positioning relative to the end of the file
SEEK_SET
An integer which may be passed to the fseek() function to request positioning relative to the beginning of the file
TMP_MAX
The maximum number of unique filenames generable by the tmpnam() function; will be at least 25
Variablesedit
Variables defined in the <stdio.h> header include:
A pointer to a FILE which refers to the standard error stream, often a display terminal.
Member typesedit
Data types defined in the <stdio.h> header include:
FILE – also known as a file handle or a 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)
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
size_t – an unsigned integer type which is the type of the result of the sizeof operator.
Extensionsedit
The POSIX standard defines several extensions to stdio in its Base Definitions, among which are a readline function that allocates memory, the fileno and fdopen functions that establish the link between FILE objects and file descriptors, and a group of functions for creating FILE objects that refer to in-memory buffers.[5]
Exampleedit
The following C program opens a binary file called myfile, reads five bytes from it, and then closes the file.
#include<stdio.h>#include<stdlib.h>intmain(void){charbuffer[5];FILE*fp=fopen("myfile","rb");if(fp==NULL){perror("Failed to open file \"myfile\"");returnEXIT_FAILURE;}if(fread(buffer,1,5,fp)<5){fputs("An error occurred while reading the file.\n",stderr);returnEXIT_FAILURE;}fclose(fp);printf("The bytes read were: ");for(inti=0;i<5;++i){printf("%02X ",buffer[i]);}putchar('\n');returnEXIT_SUCCESS;}
Several alternatives to stdio have been developed. Among these is the C++ iostream library, part of the ISO C++ standard. ISO C++ still requires the stdio functionality.
Other alternatives include the Sfio[6] (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 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.[7] It was released to the outside world in 1997, and the last release was 1 February 2005.[8]
^McIlroy, M. D. (1987). A Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986(PDF) (Technical report). CSTR. Bell Labs. 139.
^"(stdio.h) - C++ Reference". C++. Retrieved 25 July 2021.
^. Archived from the original on 11 February 2006. Retrieved 16 March 2021.{{cite web}}: CS1 maint: bot: original URL status unknown (link)
^Korn, David G.; Vo, Kiem-Phong (1991). SFIO: Safe/Fast String/File IO. Proc. Summer USENIX Conf. CiteSeerX10.1.1.51.6574.
^Fowler, Glenn S.; Korn, David G.; Vo, Kiem-Phong (2000). Extended Formatting with Sfio. Proc. Summer USENIX Conf.
External linksedit
The Wikibook C Programming has a page on the topic of: C Programming/C Reference
Media related to C file input/output at Wikimedia Commons
January 01, 1970
file, input, output, programming, language, provides, many, standard, library, functions, file, input, output, these, functions, make, bulk, standard, library, header, stdio, functionality, descends, from, portable, package, written, mike, lesk, bell, labs, ea. The C programming language provides many standard library functions for file input and output These functions make up the bulk of the C standard library header lt stdio h gt 1 The functionality descends from a portable I O package written by Mike Lesk at Bell Labs in the early 1970s 2 and officially became part of the Unix operating system in Version 7 3 The I O functionality of C is fairly low level by modern standards C abstracts all file operations into operations on streams of bytes which may be input streams or output streams Unlike some earlier programming languages C has no direct support for random access data files to read from a record in the middle of a file the programmer must create a stream seek to the middle of the file and then read bytes in sequence from the stream The stream model of file I O was popularized by Unix which was developed concurrently with the C programming language itself The vast majority of modern operating systems have inherited streams from Unix and many languages in the C programming language family have inherited C s file I O interface with few if any changes for example PHP Contents 1 Overview 1 1 Functions 1 2 Constants 1 3 Variables 1 4 Member types 1 5 Extensions 2 Example 3 Alternatives to stdio 4 See also 5 References 6 External linksOverview editThis 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 4 Functions edit Most of the C file input output functions are defined in lt stdio h gt or in the C header cstdio which contains the standard C functionality but in the std namespace Bytecharacter Widecharacter Description File access fopen Opens a file with a non Unicode filename on Windows and possible UTF 8 filename on Linux freopen Opens a different file with an existing stream fflush Synchronizes an output stream with the actual file fclose Closes a file setbuf Sets the buffer for a file stream setvbuf Sets the buffer and its size for a file stream fwide Switches a file stream between wide character I O and narrow character I O Direct input output fread Reads from a file fwrite Writes to a file Unformatted input output fgetcgetc fgetwcgetwc Reads a byte wchar t from a file stream fgets fgetws Reads a byte wchar t line from a file stream fputcputc fputwcputwc Writes a byte wchar t to a file stream fputs fputws Writes a byte wchar t string to a file stream getchar getwchar Reads a byte wchar t from stdin gets Reads a byte string from stdin until a newline or end of file is encountered deprecated in C99 removed from C11 putchar putwchar Writes a byte wchar t to stdout puts Writes a byte string to stdout ungetc ungetwc Puts a byte wchar t back into a file stream Formatted input output scanffscanfsscanf wscanffwscanfswscanf Reads formatted byte wchar t input from stdin a file stream or a buffer vscanfvfscanfvsscanf vwscanfvfwscanfvswscanf Reads formatted input byte wchar t from stdin a file stream or a buffer using variable argument list printffprintfsprintfsnprintf wprintffwprintfswprintf Prints formatted byte wchar t output to stdout a file stream or a buffer vprintfvfprintfvsprintfvsnprintf vwprintfvfwprintfvswprintf Prints formatted byte wchar t output to stdout a file stream or a buffer using variable argument list perror Writes a description of the current error to stderr File positioning ftellftello Returns the current file position indicator fseekfseeko Moves the file position indicator to a specific location in a file fgetpos Gets the file position indicator fsetpos Moves the file position indicator to a specific location in a file rewind Moves the file position indicator to the beginning in a file Errorhandling clearerr Clears errors feof Checks for the end of file ferror Checks for a file error Operations on files remove Erases a file rename Renames a file tmpfile Returns a pointer to a temporary file tmpnam Returns a unique filename Constants edit Constants defined in the lt stdio h gt header include Name Notes EOF A negative integer of type int used to indicate end of file conditions BUFSIZ An integer which is the size of the buffer used by the setbuf function FILENAME MAX The size of a char array which is large enough to store the name of any file that can be opened FOPEN MAX The number of files that may be open simultaneously will be at least eight IOFBF An abbreviation for input output fully buffered it is an integer which may be passed to the setvbuf function to request block buffered input and output for an open stream IOLBF An abbreviation for input output line buffered it is an integer which may be passed to the setvbuf function to request line buffered input and output for an open stream IONBF An abbreviation for input output not buffered it is an integer which may be passed to the setvbuf function to request unbuffered input and output for an open stream L tmpnam The size of a char array which is large enough to store a temporary filename generated by the tmpnam function NULL A macro expanding to the null pointer constant that is a constant representing a pointer value which is guaranteed not to be a valid address of an object in memory SEEK CUR An integer which may be passed to the fseek function to request positioning relative to the current file position SEEK END An integer which may be passed to the fseek function to request positioning relative to the end of the file SEEK SET An integer which may be passed to the fseek function to request positioning relative to the beginning of the file TMP MAX The maximum number of unique filenames generable by the tmpnam function will be at least 25 Variables edit nbsp Variables defined in the lt stdio h gt header include Name Notes stdin A pointer to a FILE which refers to the standard input stream usually a keyboard stdout A pointer to a FILE which refers to the standard output stream usually a display terminal stderr A pointer to a FILE which refers to the standard error stream often a display terminal Member types edit Data types defined in the lt stdio h gt header include FILE also known as a file handle or a 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 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 size t an unsigned integer type which is the type of the result of the sizeof operator Extensions edit The POSIX standard defines several extensions to stdio in its Base Definitions among which are a readline function that allocates memory the fileno and fdopen functions that establish the link between FILE objects and file descriptors and a group of functions for creating FILE objects that refer to in memory buffers 5 Example editThe following C program opens a binary file called myfile reads five bytes from it and then closes the file include lt stdio h gt include lt stdlib h gt 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 lt 5 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 lt 5 i printf 02X buffer i putchar n return EXIT SUCCESS Alternatives to stdio edit Sfio redirects here For other uses of SFIO see SFIO disambiguation Several alternatives to stdio have been developed Among these is the C iostream library part of the ISO C standard ISO C still requires the stdio functionality Other alternatives include the Sfio 6 A Safe Fast I O Library library from AT amp T Bell Laboratories This library introduced in 1991 aimed to avoid inconsistencies unsafe practices and inefficiencies in the design of 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 7 It was released to the outside world in 1997 and the last release was 1 February 2005 8 See also editprintf format string scanf format stringReferences edit ISO IEC 9899 1999 specification p 274 7 19 Kernighan Brian Pike Rob 1984 The UNIX Programming Environment Englewood Cliffs Prentice Hall p 200 McIlroy M D 1987 A Research Unix reader annotated excerpts from the Programmer s Manual 1971 1986 PDF Technical report CSTR Bell Labs 139 stdio h C Reference C Retrieved 25 July 2021 stdio h Base Definitions Reference The Single UNIX Specification Version 4 from The Open Group Sfio A Safe Fast I O Library Archived from the original on 11 February 2006 Retrieved 16 March 2021 a href Template Cite web html title Template Cite web cite web a CS1 maint bot original URL status unknown link Korn David G Vo Kiem Phong 1991 SFIO Safe Fast String File IO Proc Summer USENIX Conf CiteSeerX 10 1 1 51 6574 Fowler Glenn S Korn David G Vo Kiem Phong 2000 Extended Formatting with Sfio Proc Summer USENIX Conf External links edit nbsp The Wikibook C Programming has a page on the topic of C Programming C Reference nbsp Media related to C file input output at Wikimedia Commons Retrieved from https en wikipedia org w index php title C file input output amp oldid 1210894765 gets, wikipedia, wiki, book, books, library,