Document revision date: 15 July 2002

Converts a local-time structure into time since the Epoch.

Format

#include <time.h>

time_t mktime (struct tm *timeptr);

Argument

timeptr

A pointer to the local-time structure.

Description

The mktime function converts the local-time structure, pointed to by timeptr, to a time in seconds since the Epoch in the same manner as the values returned by the time function. If the local time cannot be encoded, then mktime returns the value ( time_t )( - 1).

The time_t type is defined in the <time.h> header file as follows:

typedef unsigned long int time_t;

Local time-zone information is set as if mktime called tzset .

If the tm_isdst field in the local-time structure pointed to by timeptr is positive, mktime initially presumes that Daylight Savings Time (DST) is in effect for the specified time.

If tm_isdst is 0, mktime initially presumes that DST is not in effect.

If tm_isdst is negative, mktime attempts to determine whether or not DST is in effect for the specified time.

Return Values

x	The specified calendar time encoded as a value of type time_t .
( time_t )( - 1)	If the local time cannot be encoded. Be aware that a return value of ( time_t )( - 1) can also represent the valid date: Sun Feb 7 06:28:15 2106.

Maps file system object into virtual memory.

Format

#include <types.h>

#include <mman.h>

void mmap (void *addr, size_t len, int prot, int flags, int filedes, off_t off); (X/OPEN, POSIX-1)

void mmap (void *addr, size_t len, int prot, int flags, int filedes, off_t off ...); (COMPAQ C EXTENSION)

Arguments

addr

The starting address of the new region (truncated to a page boundary).

len

The length in bytes of the new region (rounded up to a page boundary).

prot

Access permission, as defined in the <mman.h> header file. Specify either PROT_NONE, PROT_READ, or PROT_WRITE.

flags

Attributes of the mapped region as the results of a bitwise-inclusive OR operation on any combination of the following:

• MAP_FILE or MAP_ANONYMOUS
• MAP_VARIABLE or MAP_FIXED
• MAP_SHARED or MAP_PRIVATE

filedes

The file that you want to map to the new mapped file region returned by the open function.

off

The offset, specified in bytes. The off_t data type is either a 64-bit integer or a 32-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 as follows:

CC/DEFINE=_LARGEFILE

...

An optional integer specifying additional flags for the SYS$CRMPSC system service for MAP_SHARED. This optional argument (Compaq C Extension) of the mmap function was introduced in OpenVMS Version 7.2.

Description

The mmap function creates a new mapped file region, a new private region, or a new shared memory region.

Your application must ensure correct synchronization when using mmap in conjunction with any other file access method, such as read and write , and standard input/output.

Before calling mmap , the calling application must also ensure that all bytes in the range [off, off+len] are written to the file (using the fsync function, for example). If this requirement is not met, mmap fails with errno set to ENXIO (No such device or address).

The addr and len arguments specify the requested starting address and length in bytes for the new region. The address is a multiple of the page size returned by sysconf(_SC_PAGE_SIZE) .

If the len argument is not a multiple of the page size returned by sysconf(_SC_PAGE_SIZE) , then the result of any reference to an address between the end of the region and the end of the page containing the end of the region is undefined.

The flags argument specifies attributes of the mapped region. Values for flags are constructed by a bitwise-inclusive OR operation on the flags from the following list of symbolic names defined in the <mman.h> header file:

MAP_FILE	Create a mapped file region.
MAP_ANONYMOUS	Create an unnamed memory region.
MAP_VARIABLE	Place region at the computed address.
MAP_FIXED	Place region at fixed address.
MAP_SHARED	Share changes.
MAP_PRIVATE	Changes are private.

The MAP_FILE and MAP_ANONYMOUS flags control whether the region you want to map is a mapped file region or an anonymous shared memory region. One of these flags must be selected.

If MAP_FILE is set in the flags argument:

• A new mapped file region is created, mapping the file associated with the filedes argument.
• The off argument specifies the file byte offset where the mapping starts. This offset must be a multiple of the page size returned by sysconf(_SC_PAGE_SIZE) .
• If the end of the mapped file region is beyond the end of the file, the result of any reference to an address in the mapped file region corresponding to an offset beyond the end of the file is unspecified.

If MAP_ANONYMOUS is set in the flags argument:

• A new memory region is created and initialized to all zeros.
• If the filedes argument is not - 1, the mmap function fails.

The new region is placed at the requested address if the requested address is not null and it is possible to place the region at this address. When the requested address is null or the region cannot be placed at the requested address, the MAP_VARIABLE and MAP_FIXED flags control the placement of the region. One of these flags must be selected.

If MAP_VARIABLE is set in the flags argument:

• If the requested address is null or if it is not possible for the system to place the region at the requested address, the region is placed at an address selected by the system.

If MAP_FIXED is set in the flags argument:

• If the requested address is not null, the mmap function succeeds even if the requested address is already part of another region. (If the address is within an existing region, the effect on the pages within that region and within the area of the overlap produced by the two regions is the same as if they were unmapped. In other words, whatever is mapped between addr and addr + len is unmapped.)
• If the requested address is null and MAP_FIXED is specified, the results are undefined.

The MAP_PRIVATE and MAP_SHARED flags control the visibility of modifications to the mapped file or shared memory region. One of these flags must be selected.

If MAP_SHARED is set in the flags argument:

• If the region is a mapped region, modifications to the region are visible to other processes that mapped the same region using MAP_SHARED.
• If the region is a mapped file region, modifications to the region are written to the file. (Note that the modifications are not immediately written to the file because of buffer cache delay; that is, the write to the file does not occur until there is a need to reuse the buffer cache. If the modifications must be written to the file immediately, use the msync function to ensure that this is done.)

If MAP_PRIVATE is set in the flags argument:

• Modifications to the mapped region by the calling process are not visible to other processes that mapped the same region using either MAP_PRIVATE or MAP_SHARED.
• Modifications to the mapped region by the calling process are not written to the file.

It is unspecified whether modifications by processes that mapped the region using MAP_SHARED are visible to other processes that mapped the same region using MAP_PRIVATE.

The prot argument specifies access permissions for the mapped region. Specify one of the following:

PROT_NONE	No access
PROT_READ	Read-only
PROT_WRITE	Read/Write access

After the successful completion of the mmap function, you can close the filedes argument without effect on the mapped region or on the contents of the mapped file. Each mapped region creates a file reference, similar to an open file descriptor, that prevents the file data from being deallocated.

Note The following rules apply to OpenVMS specific file references: Because of the additional file reference, if filedes is not opened for file sharing, mmap reopens it with file sharing enabled. The additional file reference that remains for mapped regions implies that a later open , fopen , or create call to the file that is mapped must specify file sharing.

Modifications made to the file using the write function are visible to mapped regions, and modifications to a mapped region are visible with the read function.

Note Beginning with OpenVMS Version 7.2, while processing a MAP_SHARED request, the mmap function constructs the flags argument of the SYS$CRMPSC service as a bitwise inclusive OR of those bits it sets by itself to fulfill the MAP_SHARED request and those bits specified by the caller in the optional argument. By default, for MAP_SHARED the mmap function creates a temporary group global section. The optional mmap argument provides the caller with direct access to the features of the SYS$CRMPSC system service. Using the optional argument, the caller can create, for example, a system global section (SEC$M_SYSGBL bit) or permanent global section (SEC$M_PERM bit). For example, to create a system permanent global section, the caller can specify (SEC$M_SYSGBL | SEC$M_PERM) in the optional argument. The mmap function does not check or set any privileges. It is the responsibility of the caller to set appropriate privileges, such as SYSGBL privilege for SEC$M_SYSGBL, and PRMGBL for SEC$M_PERM, before calling mmap with the optional argument.

See also read , write , open , fopen , creat , and sysconf in this section.

Return Values

x

The address where the mapping is placed.

MAP_FAILED

Indicates an error; errno is set to one of the following values: EACCES -- The file referred to by filedes is not open for read access, or the file is not open for write access and PROT_WRITE was set for a MAP_SHARED mapping operation. EBADF -- The filedes argument is not a valid file descriptor. EINVAL --The flags or prot argument is invalid, or the addr argument or off argument is not a multiple of the page size returned by sysconf(_SC_PAGE_SIZE) . Or MAP_ANONYMOUS was specified in flags and filedes is not - 1. ENODEV -- The file descriptor filedes refers to an object that cannot be mapped, such as a terminal. ENOMEM -- There is not enough address space to map len bytes. ENXIO -- The addresses specified by the range [ off, off + len] are invalid for filedes. EFAULT -- The addr argument is an invalid address.

Decomposes a floating-point number.

Format

#include <math.h>

double modf (double x, double *iptr);

float modff (float x, float *iptr); (ALPHA ONLY)

long double modfl (long double x, long double *iptr); (ALPHA ONLY)

Arguments

x

An object of type double , float , or long double .

iptr

A pointer to an object of type double , float , or long double to match the type of x.

Description

The modf functions decompose their first argument x into a positive fractional part f and an integer part i, each of which has the same sign as x.

The functions return f and assign i to the object pointed to by the second argument (iptr).

Return Values

x	The fractional part of the argument x.
NaN	x is NaN; errno is set to EDOM and * iptr is set to NaN.
0	Underflow occurred; errno is set to ERANGE.

Change the current cursor position on the specified window to the coordinates (y,x). The move function acts on the stdscr window.

Format

#include <curses.h>

int move (int y, int x);

int wmove (WINDOW *win, int y, int x);

Arguments

win

A pointer to the window.

y

A window coordinate.

x

A window coordinate.

Description

For more information, see the scrollok function in this section.

Return Values

OK	Indicates success.
ERR	Indicates that the function makes the screen scroll illegally.

Modifies access protections of memory mapping.

Format

#include <mman.h>

int mprotect (void *addr, size_t len, int prot);

Arguments

addr

The address of the region that you want to modify.

len

The length in bytes of the region that you want to modify.

prot

Access permission, as defined in the <mman.h> header file. Specify either PROT_NONE, PROT_READ, or PROT_WRITE.

Description

The mprotect function modifies the access protection of a mapped file or shared memory region.

The addr and len arguments specify the address and length in bytes of the region that you want to modify. The len argument must be a multiple of the page size as returned by sysconf(_SC_PAGE_SIZE) . If len is not a multiple of the page size as returned by sysconf(_SC_PAGE_SIZE) , the length of the region is rounded up to the next multiple of the page size.

The prot argument specifies access permissions for the mapped region. Specify one of the following:

PROT_NONE	No access
PROT_READ	Read-only
PROT_WRITE	Read/Write access

The mprotect function does not modify the access permission of any region that lies outside of the specified region, except that the effect on addresses between the end of the region, and the end of the page containing the end of the region, is unspecified.

If the mprotect function fails under a condition other than that specified by EINVAL, the access protection of some of the pages in the range [addr, addr + len] can change. Suppose the error occurs on some page at an addr2; mprotect can modify protections of all whole pages in the range [addr, addr2].

See also sysconf in this section.

Return Values

0	Indicates success.
- 1	Indicates an error; errno is set to one of the following values: EACCESS -- The prot argument specifies a protection that conflicts with the access permission set for the underlying file. EINVAL -- The prot argument is invalid, or the addr argument is not a multiple of the page size as returned by sysconf(_SC_PAGE_SIZE) . EFAULT -- The range [ addr, addr + len] includes an invalid address.

Generates uniformly distributed pseudorandom-number sequences. Returns 48-bit signed long integers.

Format

#include <stdlib.h>

long int mrand48 (void);

Description

The mrand48 function generates pseudorandom numbers using the linear congruential algorithm and 48-bit integer arithmetic.

It returns signed long integers uniformly distributed over the range of y values such that -2³¹ <= y < 2³¹ .

Before you call the mrand48 function, use either srand48 , seed48 , or lcong48 to initialize the random-number generator. You must initialize the mrand48 function prior to invoking it, because it stores the last 48-bit Xi generated into an internal buffer. (Although it is not recommended, constant default initializer values are supplied automatically if the drand48 , lrand48 , or mrand48 functions are called without first calling an initialization function.)

The function works by generating a sequence of 48-bit integer values, Xi, according to the linear congruential formula:

Xn+1 = (aXn+c)mod m n >= 0

The argument m equals 2⁴⁸ , so 48-bit integer arithmetic is performed. Unless you invoke the lcong48 function, the multiplier value a and the addend value c are:

a = 5DEECE66D16 = 2736731631558 c = B16 = 138

The values returned by the mrand48 function is computed by first generating the next 48-bit Xi in the sequence. Then the appropriate bits, according to the type of returned data item, are copied from the high-order (most significant) bits of Xi and transformed into the returned value.

See also drand48 , lrand48 , lcong48 , seed48 , and srand48 in this section.

Return Values

n	Returns signed long integers uniformly distributed over the range -2 31 <= y < 2 31 .

	privacy and legal statement
5763PRO_040.HTML