Writes a character to a specified file.

Format

#include <stdio.h>

int fputc (int character, FILE *file_ptr);

Arguments

character

An object of type int .

file_ptr

A file pointer.

Description

This function writes a single character to a file and returns the character. See also putc in this section.

Return Values

x	The character written to the file. Indicates success.
EOF	Indicates an output error.

Writes a character string to a file without copying the string's null terminator (\0).

Format

#include <stdio.h>

int fputs (const char *str, FILE *file_ptr);

Arguments

str

A pointer to a character string.

file_ptr

A file pointer.

Description

See also puts in this section. Unlike puts , the fputs function does not append a new-line character to the output string.

Return Values

Nonnegative value	Indicates success.
EOF	Indicates an error.

Converts a wide character to its corresponding multibyte value, and writes the result to a specified file.

Format

#include <wchar.h>

wint_t fputwc (wint_t wc, FILE *file_ptr);

Arguments

wc

An object of type wint_t .

file_ptr

A file pointer.

Description

This function writes a wide character to a file and returns the character. See also putwc in this section.

Return Values

x

The character written to the file. Indicates success.

WEOF

Indicates an output error. The function sets errno to the following: EILSEQ -- Invalid wide-character code detected. The function can also set errno to the following as a result of errors returned from the I/O subsystem: EBADF -- The file descriptor is not valid. EIO -- I/O error. ENOSPC -- No free space on the device containing the file. ENXIO -- Device does not exist. EPIPE -- Broken pipe. ESPIPE -- Illegal seek in a file opened for append. EVMSERR -- Non-translatable VMS error. vaxc$errno contains the VMS error code. This indicates that an I/O error occurred for which there is no equivalent C error code.

Writes a wide-character string to a file without copying the null terminating character.

Format

#include <wchar.h>

int fputws (const wchar_t *wstr, FILE *file_ptr);

Arguments

wstr

A pointer to a wide-character string.

file_ptr

A file pointer.

Description

The function converts the specified wide-character string to a multibyte character string and writes it to the specified file. The function does not append a terminating null byte corresponding to the null wide-character to the output string.

Return Values

Nonnegative value	Indicates success.
--1	Indicates an error. The function sets errno . For a list of the values see fputwc in this section.

Reads a specified number of items from the file.

Format

#include <stdio.h>

size_t fread (void *ptr, size_t size_of_item, size_t number_items, FILE *file_ptr);

Arguments

ptr

A pointer to the location, within memory, where you place the information being read. The type of the object pointed to is determined by the type of the item being read.

size_of_item

The size of the items being read, in bytes.

number_items

The number of items to be read.

file_ptr

A pointer that indicates the file from which the items are to be read.

Description

The type size_t is defined in the header file <stdio.h> as follows:

typedef unsigned int size_t

The reading begins at the current location in the file. The items read are placed in storage beginning at the location given by the first argument. You must also specify the size of an item, in bytes.

If the file pointed to by file_ptr was opened in record mode, fread will read size_of_item multiplied by number_items bytes from the file. That is, it does not necessarily read number_items records.

Return Values

n	The number of bytes read divided by size_of_item.
0	Indicates the end-of-file or an error.

Makes available for reallocation the area allocated by a previous calloc , malloc , or realloc call.

Format

#include <stdlib.h>

void free (void *ptr);

Argument

ptr

The address returned by a previous call to malloc , calloc , or realloc . If ptr is a NULL pointer, no action occurs.

Description

The ANSI C standard defines free as not returning a value; therefore, the function prototype for free is declared with a return type of void . However, since a free can fail, and since previous versions of the Compaq C RTL have declared free to return an int , the implementation of free does return 0 on success and --1 on failure.

Substitutes the file named by a file specification for the open file addressed by a file pointer. The latter file is closed.

Format

#include <stdio.h>

FILE *freopen (const char *file_spec, const char *a_mode, FILE *file_ptr, ...);

Arguments

file_spec

A pointer to a string that contains a valid OpenVMS or UNIX style file specification. After the function call, the given file pointer is associated with this file.

a_mode

The access mode indicator. See the fopen function in this section for a description.

file_ptr

A file pointer.

...

Optional file attribute arguments. The file attribute arguments are the same as those used in the creat function.

Description

This function is typically used to associate one of the predefined names stdin, stdout, or stderr with a file. For more information about these predefined names, see Chapter 2.

Return Values

file_ptr	The file pointer, if freopen is successful.
NULL	Indicates an error.

Calculates the fractional and exponent parts of a floating-point value.

Format

#include <math.h>

double frexp (double value, int *eptr);

float frexp (float value, int *eptr); (ALPHA ONLY)

long double frexp (long double value, int *eptr); (ALPHA ONLY)

Arguments

value

A floating-point number of type double , float , or long double .

eptr

A pointer to an int where frexp places the exponent.

Description

The frexp functions break the floating-point number (value) into a normalized fraction and an integral power of 2, as follows:

value = fraction * (2exp)

The fractional part is returned as the return value. The exponent is placed in the integer variable pointed to by eptr.

Example

#include <math.h> main () { double val = 16.0, fraction; int exp; fraction = frexp(val, &exp); printf("fraction = %f\n",fraction); printf("exp = %d\n",exp); }

In this example, frexp converts the value 16 to .5 * 2 ⁵ . The example produces the following output:

fraction = 0.500000 exp = 5

|value| = Infinity or NaN is an invalid argument.

Return Value

x	The fractional part of value.
0	Both parts of the result are 0.
NaN	If value is NaN, NaN is returned, errno is set to EDOM, and the value of * eptr is unspecified.
value	If | value| = Infinity, value is returned, errno is set to EDOM, and the value of * eptr is unspecified.

Performs formatted input from a specified file, interpreting it according to the format specification.

Format

#include <stdio.h>

int fscanf (FILE *file_ptr, const char *format_spec, ...);

Arguments

file_ptr

A pointer to the file that provides input text.

format_spec

A pointer to a character string that contains the format specification. For more information on conversion characters, see Chapter 2.

...

Optional expressions whose results correspond to conversion specifications given in the format specification.

If no conversion specifications are given, you can omit the input pointers. Otherwise, the function calls must have exactly as many input pointers as there are conversion specifications, and the conversion specifications must match the types of the input pointers.

Conversion specifications are matched to input sources in left-to-right order. Excess input pointers, if any, are ignored.

Description

An example of a conversion specification follows:

#include <stdio.h> main () { int temp, temp2; fscanf(stdin, "%d %d", &temp, &temp2); printf("The answers are %d, and %d.", temp, temp2); }

Consider a file, designated by stdin, with the following contents:

4 17

The example conversion specification produces the following result:

The answers are 4, and 17.

For a complete description of the format specification and the input pointers, see Chapter 2.

Return Values

x

The number of successfully matched and assigned input items.

EOF

Indicates that the end-of-file was encountered or a read error occurred. If a read error occurs, the function sets errno to one of the following: EILSEQ -- Invalid character detected. EVMSERR -- Non-translatable VMS error. vaxc$errno contains the VMS error code. This can indicate that conversion to a numeric value failed due to overflow. The function can also set errno to the following as a result of errors returned from the I/O subsystem: EBADF -- The file descriptor is not valid. EIO -- I/O error. ENXIO -- Device does not exist. EPIPE -- Broken pipe. EVMSERR -- Non-translatable VMS error. vaxc$errno contains the VMS error code. This indicates that an I/O error occurred for which there is no equivalent C error code.

Positions the file to the specified byte offset in the file.

Format

#include <stdio.h>

int fseek (FILE *file_ptr, long int offset, int direction);

Arguments

file_ptr

A file pointer.

offset

The offset, specified in bytes.

direction

An integer indicating the position to which the offset is added to calculate the new position. The new position is the beginning of the file if direction is SEEK_SET, the current value of the file position indicator if direction is SEEK_CUR, or end-of-file if direction is SEEK_END.

Description

This function can position fixed-length record-access file with no carriage control or a stream-access file on any byte offset, but can position all other files only on record boundaries.

The available Standard I/O functions position a variable-length or VFC record file at its first byte, at the end-of-file, or on a record boundary. Therefore, the arguments given to fseek must specify any of the following:

• The beginning or end of the file
• A 0 offset from the current position (an arbitrary record boundary)
• The position returned by a previous, valid ftell call

See the fgetpos and fsetpos functions for a portable way to seek to arbitrary locations with these types of record files.

CAUTION If, while accessing a stream file, you seek beyond the end-of-file and then write to the file, the fseek function creates a hole by filling the skipped bytes with zeros. In general, for record files, fseek should only be directed to an absolute position that was returned by a previous valid call to ftell , or to the beginning or end of a file. If a call to fseek does not satisfy these conditions, the results are unpredictable.

See also open , creat , dup , dup2 , and lseek in this section.

Return Values

0	Indicates successful seeks.
--1	Indicates improper seeks.

Positions the file to the specified byte offset in the file. Equivalent to fseek .

Format

#include <stdio.h>

int fseeko (FILE *file_ptr, off_t offset, int direction);

Arguments

file_ptr

A file pointer.

offset

The offset, specified in bytes. The off_t data type is either a 32-bit integer or 64-bit integer. The 64-bit interface allows for file sizes greater than 2 gigabytes, and can be selected at compile time by defining the _LARGEFILE feature-test macro:

CC/DEFINE=_LARGEFILE

direction

An integer indicating the position to which the offset is added to calculate the new position. The new position is the beginning of the file if direction is SEEK_SET, the current value of the file position indicator if direction is SEEK_CUR, or end-of-file if direction is SEEK_END.

Description

The fseeko function is identical to the fseek function, except that the offset argument is of type off_t instead of long int .

Sets the file position indicator for a given file.

Format

#include <stdio.h>

int fsetpos (FILE *stream, const fpos_t *pos);

Arguments

stream

A file pointer.

pos

A pointer to an implementation-defined structure. The fgetpos function fills this structure with information that can be used on subsequent calls to fsetpos .

Description

Call the fgetpos function before using the fsetpos function.

Return Values

0	Indicates success.
--1	Indicates an error.

Accesses information about the file specified by the file descriptor.

Format

#include <stat.h>

int fstat (int file_desc, struct stat *buffer);

Arguments

file_desc

A file descriptor.

buffer

A pointer to a structure of type stat_t , which is defined in the <stat.h> header file. The argument receives information about that particular file. The members of the structure pointed to by buffer are as follows:

Member	Type	Definition
st_dev	dev_t	Pointer to a physical device name
st_ino[3]	ino_t	Three words to receive the file ID
st_mode	mode_t	File "mode" (prot, dir,...)
st_nlink	nlink_t	For UNIX system compatibility only
st_uid	uid_t	Owner user ID
st_gid	gid_t	Group member: from st_uid
st_rdev	dev_t	UNIX system compatibility -- always 0
st_size	off_t	File size, in bytes
st_atime	time_t	File access time; always the same as st_mtime
st_mtime	time_t	Last modification time
st_ctime	time_t	File creation time
st_fab_rfm	char	Record format
st_fab_rat	char	Record attributes
st_fab_fsz	char	Fixed header size
st_fab_mrs	unsigned	Record size

The types dev_t , ino_t , off_t , mode_t , nlink_t , uid_t , gid_t , and time_t , are defined in the <stat.h> header file. However, when compiling for compatibility (/DEFINE=_DECC_V4_SOURCE), only dev_t , ino_t , and off_t are defined.

The off_t data type is either a 32-bit integer or 64-bit integer. The 64-bit interface allows for file sizes greater than 2 gigabytes, and can be selected at compile time by defining the _LARGEFILE feature-test macro:

CC/DEFINE=_LARGEFILE

As of OpenVMS Version 7.0, times are given in seconds since the Epoch (00:00:00 GMT, January 1, 1970).

The st_mode structure member is the status information mode and is defined in the <stat.h> header file. The st_mode bits follow:

Bits	Constant	Definition
0170000	S_IFMT	Type of file
0040000	S_IFDIR	Directory
0020000	S_IFCHR	Character special
0060000	S_IFBLK	Block special
0100000	S_IFREG	Regular
0030000	S_IFMPC	Multiplexed char special
0070000	S_IFMPB	Multiplexed block special
0004000	S_ISUID	Set user ID on execution
0002000	S_ISGID	Set group ID on execution
0001000	S_ISVTX	Save swapped text even after use
0000400	S_IREAD	Read permission, owner
0000200	S_IWRITE	Write permission, owner
0000100	S_IEXEC	Execute/search permission, owner

Description

This function does not work on remote network files.

Note (ALPHA ONLY) On OpenVMS Alpha systems, the stat , fstat , utime , and utimes functions have been enhanced to take advantage of the new file-system support for POSIX-compliant file timestamps. This support is available only on ODS-5 devices on OpenVMS Alpha systems beginning with a version of OpenVMS Alpha after Version 7.3. Before this change, the stat and fstat functions were setting the values of the st_ctime, st_mtime, and st_atime fields based on the following file attributes: st_ctime - ATR$C_CREDATE (file creation time) st_mtime - ATR$C_REVDATE (file revision time) st_atime - was always set to st_mtime because no support for file access time was available Also, for the file-modification time, utime and utimes were modifying the ATR$C_REVDATE file attribute, and ignoring the file-access-time argument. After the change, for a file on an ODS-5 device, the stat and fstat functions set the values of the st_ctime, st_mtime, and st_atime fields based on the following new file attributes: st_ctime - ATR$C_ATTDATE (last attribute modification time) st_mtime - ATR$C_MODDATE (last data modification time) st_atime - ATR$C_ACCDATE (last access time) If ATR$C_ACCDATE is zero, as on an ODS-2 device, the stat and fstat functions set st_atime to st_mtime. For the file-modification time, the utime and utimes functions modify both the ATR$C_REVDATE and ATR$C_MODDATE file attributes. For the file-access time, these functions modify the ATR$C_ACCDATE file attribute. Setting the ATR$C_MODDATE and ATR$C_ACCDATE file attributes on an ODS-2 device has no effect. For compatibility, the old behavior of stat , fstat , utime and utimes remains the default, regardless of the kind of device. The new behavior must be explicitly enabled at runtime by defining the DECC$EFS_FILE_TIMESTAMPS logical name to "ENABLE" before invoking the application. Setting this logical does not affect the behavior of stat , fstat , utime and utimes for files on an ODS-2 device.

Return Values

0	Indicates successful completion.
--1	Indicates an error other than a protection violation.
--2	Indicates a protection violation.