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Flushes data all the way to the disk.
#include <unistd.h>int fsync (int fd);
fd
A file descriptor corresponding to an open file.
This function behaves much like the fflush function. The primary difference between the two is that fsync flushes data all the way to the disk while fflush flushes data only as far as the underlying RMS buffers. Also, with fflush , you can flush all buffers at once; with fsync you cannot.
0 Indicates successful completion. --1 Indicates an error.
Returns the current byte offset to the specified stream file.
#include <stdio.h>long int ftell (FILE *file_ptr);
file_ptr
A file pointer.
This function measures the byte offset from the beginning of the file.For variable-length files, VFC files, or any file with carriage-control attributes, it the file is opened in record mode, then ftell returns the starting position of the current record, not the current byte offset.
When using record files, the ftell function ignores any characters that have been pushed back using either ungetc or ungetwc . This behavior does not occur if stream files are being used.
For a portable way to measure the exact offset for any type of file, see the fgetpos function.
n The current offset. EOF Indicates an error.
Returns the elapsed time since 00:00:00, January 1, 1970, in the structure pointed at by timeptr.
#include <timeb.h>Function Variants Compiling with the _DECC_V4_SOURCE and _VMS_V6_SOURCE feature-test macros defined enables a local-time-based entry point to this function that is equivalent to the behavior before OpenVMS Version 7.0.int ftime (struct timeb *timeptr);
timeptr
A pointer to the structure timeb_t .
The typedef timeb_t refers to the following structure defined in the <timeb.h> header file:
typedef struct timeb { time_t time; unsigned short millitm; short timezone; short dstflag; };The member time gives the time in seconds.
The member millitm gives the fractional time in milliseconds.
After a call to ftime , the timezone and dstflag members of the timeb structure have the values of the global variables timezone and dstflag , respectively. See the description of the tzset function for timezone and dstflag global variables.
0 Successful execution. The timeb_t structure is filled in. --1 Indicates an error. Failure might indicate that the system's time-differential factor (that is, the difference between the system time and UTC time) is not set correctly. If the value of the SYS$TIMEZONE_DIFFERENTIAL logical is wrong, the function fails with errno set to EINVAL.
Truncates a file to a specified length.
#include <unistd.h>int ftruncate (int filedes, off_t length);
filedes
The descriptor of a file that must be open for writing.length
The new length of the file in bytes.
This function truncates a file at the specified position. For record files, the position must be a record boundary. Also, the files must be local, regular files.If the file was previously larger than length, extra data is lost. If the file was previously shorter than length, bytes between the old and new lengths are read as zeros.
0 Indicates success. --1 An error occurred; errno is set to indicate the error.
Walks a file tree.
#include <ftw.h>int ftw (const char *path, int(*function)(const char *, const struct stat *,int), int depth);
path
The directory hierarchy to be searched.function
The function to be invoked for each file in the directory hierarchy.depth
The maximum number of directory streams or file descriptors, or both, available for use by ftw . This argument should be in the range of 1 to OPEN_MAX.
This function recursively searches the directory hierarchy that descends from the directory specified by the path argument.For each file in the hierarchy, ftw calls the function specified by the function argument, passes it a pointer to a null-terminated character string containing the name of the file, a pointer to a stat structure containing information about the file, and an integer.
The integer identifies the file type. Possible values, defined in <ftw.h> are:
FTW_F Regular file. FTW_D Directory. FTW_DNR Directory that cannot be read. FTW_NS A file on which stat could not successfully be executed. If the integer is FTW_DNR, then the files and subdirectories contained in that directory are not processed.
If the integer is FTW_NS, then the stat structure contents are meaningless. For example, a file in a directory for which you have read permission but not execute (search) permission can cause the function argument to pass FTW_NS.
The ftw function finishes processing a directory before processing any of its files or subdirectories.
The ftw function continues the search until:
- The directory hierarchy specified by the path argument is completed.
- An invocation of the function specified by the function argument returns a nonzero value.
- An error (such as an I/O error) is detected within the ftw function.
Because the ftw function is recursive, it is possible for it to terminate with a memory fault because of stack overflow when applied to very deep file structures.
The ftw function uses the malloc function to allocate dynamic storage during its operation. If ftw is forcibly terminated, as with a call to longjmp from the function pointed to by the function argument, ftw has no chance to free that storage. It remains allocated.
A safe way to handle interrupts is to store the fact that an interrupt has occurred, and arrange to have the function specified by the function argument return a nonzero value the next time it is called.
Note
The ftw function is reentrant; make sure that the function supplied as argument function is also reentrant.See malloc , longjump , lstat , and stat in this section.
0 Indicates success. x Indicates that the function specified by the function argument stops its search, and returns the value that was returned by the function. --1 Indicates an error; errno is set to one of the following values:
- EACCES -- Search permission is denied for any component of the path argument or read permission is denied for the path argument.
- ENAMETOOLONG -- The length of the path string exceeds PATH_MAX, or a pathname component is longer than NAME_MAX while [_POSIX_NO_TRUNC] is in effect.
- ENOENT -- The path argument points to the name of a file that does not exist or points to an empty string.
- ENOMEM -- There is insufficient memory for this operation.
Also, if the function pointed to by the function argument encounters an error, errno can be set accordingly.
Waits for I/O on a specific file to complete.
#include <stdio.h>int fwait (FILE *fp);
fp
A file pointer corresponding to an open file.
This function is used primarily to wait for completion of pending asynchronous I/O.
0 Indicates successful completion. --1 Indicates an error.
Determines and sets the orientation of a stream.
#include <wchar.h>int fwide (FILE *stream, int mode);
stream
A file pointer.mode
A value that specifies the desired orientation of the stream.
This function determines the orientation of the stream pointed to by stream and sets the orientation of a non-oriented stream according to the mode argument in the following way:
If the mode argument is Then the fwide function greater than zero makes the stream wide-oriented. less than zero makes the stream byte-oriented. zero does not alter the orientation of the stream. If the orientation of the stream has already been set, fwide does not alter it. Because no error status is defined for fwide , the calling application should check errno if fwide returns a 0.
> 0 After the call, the stream is wide-oriented. < 0 After the call, the stream is byte-oriented. 0 After the call, the stream has no orientation or a stream argument is invalid; the function sets errno .
Writes a specified number of items to the file.
#include <stdio.h>size_t fwrite (const void *ptr, size_t size_of_item, size_t number_items, FILE *file_ptr);
ptr
A pointer to the memory location from which information is being written. The type of the object pointed to is determined by the type of the item being written.size_of_item
The size, in bytes, of the items being written.number_items
The number of items to be written.file_ptr
A file pointer that indicates the file to which the items are being written.
The type size_t is defined in the header file <stdio.h> as follows:
typedef unsigned int size_tThe writing begins at the current location in the file. The items are written from 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 is a record file, the fwrite function outputs at least number_items records, each of length size_of_item.
x The number of items written. The number of records written depends upon the maximum record size of the file.
Writes output to the stream under control of the wide-character format string.
#include <wchar.h>int fwprintf (FILE *stream, const wchar_t *format, ...);
stream
A file pointer.format
A pointer to a wide-character string containing the format specifications. For more information about format and conversion specifications and their corresponding arguments, see Chapter 2....
Optional expressions whose resultant types correspond to conversion specifications given in the format specification.If no conversion specifications are given, the output sources can be omitted. Otherwise, the function calls must have exactly as many output sources as there are conversion specifications, and the conversion specifications must match the types of the output sources.
Conversion specifications are matched to output sources in left-to-right order. Any excess output sources are ignored.
This function writes output to the stream pointed to by stream under control of the wide-character string pointed to by format, which specifies how to convert subsequent arguments to output. If there are insufficient arguments for the format, the behavior is undefined. If the format is exhausted while arguments remain, the excess arguments are evaluated, but are otherwise ignored. The fwprintf function returns when it encounters the end of the format string.The format argument is composed of zero or more directives that include:
- Ordinary wide characters (not the percent sign (%))
- Conversion specifications
n The number of wide characters written. Negative value Indicates an error. The function sets errno to one of the following:
- EILSEQ -- Invalid character detected.
- EINVAL -- Insufficient arguments.
- ENOMEM -- Not enough memory available for conversion.
- ERANGE -- Floating-point calculations overflow.
- EVMSERR -- Nontranslatable VMS error. vaxc$errno contains the VMS error code. This might indicate that conversion to a numeric value failed because of 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.
- 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 -- Nontranslatable 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.
The following example shows how to print a date and time in the form "Sunday, July 3, 10:02", followed by Pi sign to five decimal places:
#include <math.h> #include <stdio.h> #include <wchar.h> /*...*/ wchar_t *weekday, *month; /* pointers to wide-character strings */ int day, hours, min; fwprintf(stdout, L"%ls, %ls %d, %.2d:%.2d\n", weekday, month, day, hour, min); fwprintf(stdout, L"pi = %.5f\n", 4 * atan(1.0));
Reads input from the stream under control of the wide-character format string.
#include <wchar.h>int fwscanf (FILE *stream, const wchar_t *format, ...);
stream
A file pointer.format
A pointer to a wide-character string containing the format specification. For more information about format and conversion specifications and their corresponding arguments, see Chapter 2....
Optional expressions whose results correspond to conversion specifications given in the format specification. For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.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.
This function reads input from the stream pointed to by stream under the control of the wide-character string pointed to by format. If there are insufficient arguments for the format, the behavior is undefined. If the format is exhausted while arguments remain, the excess arguments are evaluated, but otherwise ignored.The format is composed of zero or more directives that include:
- One or more white-space wide characters.
- An ordinary wide character (neither a percent (%)) nor a white-space wide character).
- Conversion specifications.
Each conversion specification is introduced by the wide character %.
If the stream pointed to by the stream argument has no orientation, fwscanf makes the stream wide-oriented.
n The number of input items assigned, sometimes fewer than provided for, or even zero, in the event of an early matching failure. EOF Indicates an error; input failure occurs before any conversion.
Converts its argument to a null-terminated string of ASCII digits and returns the address of the string.
#include <stdlib.h>Function Variants This function also has variants named _gcvt32 and _gcvt64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.8 for more information on using pointer-size-specific functions.char *gcvt (double value, int ndigit, char *buffer);
value
An object of type double that is converted to a null-terminated string of ASCII digits.ndigit
The number of ASCII digits to use in the converted string. If ndigit is less than 6, the value of 6 is used.buffer
A storage location to hold the converted string.
This function places the converted string in a buffer and returns the address of the buffer. If possible, gcvt produces ndigit significant digits in F-format, or if not possible, in E-format. Trailing zeros are suppressed.The ecvt , fcvt , and gcvt functions represent the following special values specified in the IEEE Standard for floating-point arithmetic:
Value Representation Quiet NaN NaNQ Signalling NaN NaNS +Infinity Infinity --Infinity --Infinity The sign associated with each of these values is stored into the sign argument. In IEEE floating-point representation, a value of 0 (zero) can be positive or negative, as set by the sign argument.
See also fcvt and ecvt in this section.
x The address of the buffer.
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