stdio.h

header

cstdio (stdio.h)

C library to perform Input/Output operations

Input and Output operations can also be performed in C++ using the C Standard Input and Output Library (cstdio, known as stdio.h in the C language). 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 an uniform way; All streams have similar properties independently of the individual characteristics of the physical media they are associated with.

Streams are handled in the cstdio library as pointers to FILE objects. A pointer to a FILE object uniquely identifies a stream, and is used as a parameter in the operations involving that stream.

There also exist three standard streams: stdin, stdout and stderr, which are automatically created and opened for all programs using the library.

Stream properties

Streams have some properties that define which functions can be used on them and how these will treat the data input or output through them. Most of these properties are defined at the moment the stream is associated with a file (opened) using the fopen function:

Read/Write Access

Specifies whether the stream has read or write access (or both) to the physical media they are associated with.

Text / Binary

Text streams are thought to represent a set of text lines, each one ending with a new-line character. Depending on the environment where the application is run some character translation may occur with text streams to adapt some special characters to the text file specifications of the environment. A binary stream, on the other hand, is a sequence of characters written or read from the physical media with no translation, having a one-to-one correspondence with the characters read or written to the stream.

Buffer

A buffer is a block of memory where data is accumulated before being physically read or written to the associated file or device. Streams can be either fully buffered, line buffered or unbuffered. On fully buffered streams, data is read/written when the buffer is filled, on line buffered streams this happens when a new-line character is encountered, and on unbuffered streams characters are intended to be read/written as soon as possible.

 

Indicators

Streams have certain internal indicators that specify their current state and which affect the behavior of some input and output operations performed on them:

Error indicator

This indicator is set when an error has occurred in an operation related to the stream. This indicator can be checked with the ferror function, and can be reset by calling either to clearerr or to any repositioning function (rewind, fseek and fsetpos).

End-Of-File indicator

When set, indicates that the last reading or writing operation performed with the stream reached the End of File. It can be checked with the feof function, and can be reset by calling either to clearerr or to any repositioning function (rewind, fseek and fsetpos).

Position indicator

It is an internal pointer of each stream which points to the next character to be read or written in the next I/O operation. Its value can be obtained by the ftell and fgetpos functions, and can be changed using the repositioning functions rewind, fseek and fsetpos.

 

Functions

Operations on files:

remove

Remove file (function )

rename

Rename file (function )

tmpfile

Open a temporary file (function)

tmpnam

Generate temporary filename (function)

File access:

fclose

Close file (function)

fflush

Flush stream (function)

fopen

Open file (function )

freopen

Reopen stream with different file or mode (function )

setbuf

Set stream buffer (function )

setvbuf

Change stream buffering (function )

Formatted input/output:

fprintf

Write formatted output to stream (function )

fscanf

Read formatted data from stream (function )

printf

Print formatted data to stdout (function )

scanf

Read formatted data from stdin (function )

sprintf

Write formatted data to string (function )

sscanf

Read formatted data from string (function )

vfprintf

Write formatted variable argument list to stream (function )

vprintf

Print formatted variable argument list to stdout (function )

vsprintf

Print formatted variable argument list to string (function )

Character input/output:

fgetc

Get character from stream (function)

fgets

Get string from stream (function )

fputc

Write character to stream (function)

fputs

Write string to stream (function)

getc

Get character from stream (function)

getchar

Get character from stdin (function)

gets

Get string from stdin (function )

putc

Write character to stream (function)

putchar

Write character to stdout (function)

puts

Write string to stdout (function)

ungetc

Unget character from stream (function)

Direct input/output:

fread

Read block of data from stream (function)

fwrite

Write block of data to stream (function)

File positioning:

fgetpos

Get current position in stream (function)

fseek

Reposition stream position indicator (function)

fsetpos

Set position indicator of stream (function)

ftell

Get current position in stream (function)

rewind

Set position indicator to the beginning (function)

Error-handling:

clearerr

Clear error indicators (function)

feof

Check End-of-File indicator (function)

ferror

Check error indicator (function)

perror

Print error message (function)

 

Macros

EOF

End-of-File (constant)

FILENAME_MAX

Maximum length of file names (constant)

NULL

Null pointer (constant)

TMP_MAX

Number of temporary files (constant)

And also _IOFBF, _IOLBF, _IONBF, BUFSIZ, FOPEN_MAX, L_tmpnam, SEEK_CUR, SEEK_END and SEEK_SET, each described with its corresponding function.

Types

FILE

Object containing information to control a stream (type )

fpos_t

Object containing information to specify a position within a file (type)

size_t

Unsigned integral type (type)