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Determines the lowest virtual address that is not used with the program.
#include <unistd.h>void *sbrk (long int incr);
incr
The number of bytes to add to the current break address.
This function adds the number of bytes specified by its argument to the current break address and returns the old break address.When a program is executed, the break address is set to the highest location defined by the program and data storage areas. Consequently, sbrk is needed only by programs that have growing data areas.
sbrk(0) returns the current break address.
x The old break address. ( void *)(--1) Indicates that the program is requesting too much memory.
Unlike other C library implementations, the Compaq C RTL memory allocation functions (such as malloc ) do not rely on brk or sbrk to manage the program heap space. Consequently, on OpenVMS systems, calling brk or sbrk can interfere with memory allocation routines. The brk and sbrk functions are provided only for compatibility purposes.
Performs formatted input from the standard input (stdin), interpreting it according to the format specification. See Chapter 2 for information on format specifiers.
#include <stdio.h>int scanf (const char *format_spec, ...);
format_spec
Characters to be taken literally from the input or converted and placed in memory at the specified input sources. For a list of conversion characters, see Chapter 2....
Optional expressions that are pointers to objects whose resultant types correspond to conversion specifications given in the format specification.If no conversion specifications are given, you can omit these input pointers. Otherwise, the function call must have at least 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.
x The number of successfully matched and assigned input items. EOF Indicates that a read error occurred prior to any successful conversions.The function sets errno . For a list of errno values set by this function, see fscanf in this section.
Perform a scanf on the window. The scanw function acts on the stdscr window.
#include <curses.h>int scanw (char *format_spec, ...);
int wscanw (WINDOW *win, char *format_spec, ...);
win
A pointer to the window.format_spec
A pointer to the format specification string....
Optional expressions that are pointers to objects whose resultant types correspond to conversion specifications given in the format specification. If no conversion specifications are given, you may omit these input pointers.Otherwise, the function call must have at least 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.
The formatting specification (format_spec) and the other arguments are identical to those used with the scanf function.The scanw and wscanw functions accept, format, and return a line of text from the terminal screen. For more information, see the scrollok and scanf functions in this section.
OK Indicates success. ERR Indicates that the function makes the screen scroll illegally or that the scan was unsuccessful.
Moves all the lines on the window up one line. The top line scrolls off the window and the bottom line becomes blank.
#include <curses.h>int scroll (WINDOW *win);
win
A pointer to the window.
OK Indicates success. ERR Indicates an error.
Sets the scroll flag for the specified window.
#include <curses.h>scrollok (WINDOW *win, bool boolf);
win
A pointer to the window.boolf
A Boolean TRUE or FALSE value. If boolf is FALSE, scrolling is not allowed. This is the default setting. The bool type is defined in the <curses.h> header file as follows:
#define bool int
Initializes a 48-bit random number generator.
#include <stdlib.h>unsigned short *seed48 (unsigned short seed_16v[3]);
seed_16v
An array of three unsigned short int that form a 48-bit seed value.
The seed48 function initializes the random number generator. You can use this function in your program before calling the drand48 , lrand48 , or mrand48 functions. (Although it is not recommended practice, constant default initializer values are supplied automatically if you call drand48 , lrand48 , or mrand48 without 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 > 0The 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 = 138The initializer function seed48 :
- Sets the value of Xi to the 48-bit value specified in the array pointed to by seed_16v.
- Returns a pointer to a 48-bit internal buffer that contains the previous value of Xi, used only by seed48 .
The returned pointer allows you to restart the pseudorandom sequence at a given point. Use the pointer to copy the previous Xi value into a temporary array. To resume where the original sequence left off, you can call seed48 with a pointer to this array.
See also drand48 , lrand48 , and mrand48 in this section.
x A pointer to a 48-bit internal buffer.
Sets the position of a directory stream.
#include <dirent.h>void seekdir (DIR *dir_pointer, long int location);
dir_pointer
A pointer to the dir structure of an open directory.location
The number of an entry relative to the start of the directory.
This function sets the position of the next readdir operation on the directory stream specified by dir_pointer to the position specified by location. The value of location should be returned from an earlier call to telldir.If the value of location was not returned by a call to the telldir function, or if there was an intervening call to the rewinddir function on this directory stream, the effect is unspecified.
The type DIR , defined in the <dirent.h> header file, represents a directory stream. A directory stream is an ordered sequence of all the directory entries in a particular directory. Directory entries represent files. You can remove files from or add files to a directory asynchronously to the operation of the readdir function.
See readdir , rewinddir , and telldir in this section.
Activate the video display attribute attr within the window. The setattr function acts on the stdscr window.
#include <curses.h>int setattr (int attr);
int wsetattr (WINDOW *win, int attr);
win
A pointer to the window.attr
One of a set of video display attributes, which are blinking, boldface, reverse video, and underlining, and are represented by the defined constants _BLINK, _BOLD, _REVERSE, and _UNDERLINE, respectively. You can set multiple attributes by separating them with a bitwise OR operator (|) as follows:
setattr(_BLINK | _UNDERLINE);
The setattr and wsetattr functions are specific to Compaq C for OpenVMS Systems and are not portable.
OK Indicates success. ERR Indicates an error.
Associates a new buffer with an input or output file and potentially modifies the buffering behavior.
#include <stdio.h>void setbuf (FILE *file_ptr, char *buffer);
file_ptr
A file pointer.buffer
A pointer to a character array, or a NULL pointer.
You can use this function after the specified file is opened but before any I/O operations are performed.If buffer is a NULL pointer, then the call is equivalent to a call to setvbuf with the same file_ptr, a NULL buffer pointer, a buffering type of _IONBF (no buffering), and a buffer size of 0.
If buffer is not a NULL pointer, then the call is equivalent to a call to setvbuf with the same file_ptr, the same buffer pointer, a buffering type of _IOFBF, and a buffer size given by the value BUFSIZ (defined in <stdio.h> ). You should, therefore, use BUFSIZ to allocate the buffer argument used in the call to setbuf . For example:
#include <stdio.h> . . . char my_buf[BUFSIZ]; . . . setbuf(stdout, my_buf); . . .User programs must not depend on the contents of buffer once I/O has been performed on the stream. The Compaq C RTL might or might not use buffer for any given I/O operation.
The setbuf function originally allowed programmers to substitute larger buffers in place of the system default buffers in obsolete versions of UNIX. The large default buffer sizes in modern implementations of C make the use of this function unnecessary most of the time. The setbuf function is retained in the ANSI C standard for compatibility with old programs. New programs should use setvbuf instead, because it allows the programmer to bind the buffer size at run time instead of compile time, and it returns a testable result value.
Inserts or resets the environment variable name in the current environment list.
#include <stdlib.h>int setenv (const char *name, const char *value, int overwrite);
name
A variable name in the environment variable list.value
The value for the environment variable.overwrite
A value of 0 or 1 indicating whether to reset the environment variable, if it exists.
This function inserts or resets the environment variable name in the current environment list. If the variable name does not exist in the list, it is inserted with the value argument. If the variable does exist, the overwrite argument is tested. When the overwrite argument value is:
- 0 (zero) -- then the variable is not reset.
- 1 -- then the variable is reset to value.
0 Indicates success. --1 Indicates an error. errno is set to ENOMEM---Not enough memory available to expand the environment list.
Implemented for program portability and serves no function. It returns 0 (to indicate success).
#include <unistd.h>int setgid (__gid_t group_number); (_DECC_V4_SOURCE)
gid_t setgid (gid_t group_number); (NOT _DECC_V4_SOURCE)
group_number
The group number.
This function is implemented for program portability and serves no function. It returns 0 (to indicate success).
Note (ALPHA ONLY)
On OpenVMS Alpha systems, this function has been enhanced to take advantage of the new OpenVMS support for POSIX-style user, group, and session IDs available on a version of OpenVMS Alpha after Version 7.3.
The new functionality, based on PERSONA VMS services, is the default on those versions of OpenVMS Alpha where the underlying operating system support is available.
If the process has appropriate privileges, the setuid function sets the real user ID, effective user ID, and the saved set-user-ID to uid.
If the process does not have appropriate privileges but uid is equal to the real user ID or to the saved set-user-ID, then the setuid function sets the effective user ID to uid. The real user ID and saved set-user-ID remain unchanged.
To request the old behavior, define the DECC$GETJPI_BASED_UID logical name to "ENABLE":
$ DEFINE DECC$GETJPI_BASED_UID ENABLE
Sets the value of interval timers.
#include <time.h>int setitimer (int which, struct itimerval *value, struct itimerval *ovalue);
which
The type of interval timer. The Compaq C RTL only supports ITIMER_REAL.value
A pointer to an itimerval structure whose members specify a timer interval and the time left to the end of the interval.ovalue
A pointer to an itimerval structure whose members specify a current timer interval and the time left to the end of the interval.
This function sets the timer specified by which to the value specified by value, returning the previous value of the timer if ovalue is nonzero.A timer value is defined by the itimerval structure:
struct itimerval { struct timeval it_interval; struct timeval it_value; };The value of the itimerval structure members are: as follows
itimerval Member Value Meaning it_interval = 0 Disables a timer after its next expiration (Assumes it_value is nonzero). it_interval = nonzero Specifies a value used in reloading it_value when the timer expires. it_value = 0 Disables a timer. it_value = nonzero Indicates the time to the next timer expiration. Time values smaller than the resolution of the system clock are rounded up to this resolution.
The getitimer function provides one interval timer, defined in the <time.h> header file as ITIMER_REAL. This timer decrements in real time. When the timer expires, it delivers a SIGALARM signal.
Note
The interaction between setitimer and any of alarm , sleep , or usleep is unspecified.
0 Indicates success. --1 An error occurred; errno is set to indicate the error.
Provides a way to transfer control from a nested series of function invocations back to a predefined point without returning normally. It does not use a series of return statements. The setjmp function saves the context of the calling function in an environment buffer.
#include <setjmp.h>int setjmp (jmp_buf env);
env
The environment buffer, which must be an array of integers long enough to hold the register context of the calling function. The type jmp_buf is defined in the <setjmp.h> header file. The contents of the general-purpose registers, including the program counter (PC), are stored in the buffer.
When setjmp is first called, it returns the value 0. If longjmp is then called, naming the same environment as the call to setjmp , control is returned to the setjmp call as if it had returned normally a second time. The return value of setjmp in this second return is the value supplied by you in the longjmp call. To preserve the true value of setjmp , the function calling setjmp must not be called again until the associated longjmp is called.The setjmp function preserves the hardware general purpose registers, and the longjmp function restores them. After a longjmp , all variables have their values as of the time of the longjmp except for local automatic variables not marked volatile . These variables have indeterminate values.
The setjmp and longjmp functions rely on the OpenVMS condition-handling facility to effect a nonlocal goto with a signal handler. The longjmp function is implemented by generating a Compaq C RTL specified signal that allows the OpenVMS condition-handling facility to unwind back to the desired destination.
The Compaq C RTL must be in control of signal handling for any Compaq C image. For Compaq C to be in control of signal handling, you must establish all exception handlers through a call to the VAXC$ESTABLISH function. See Section 4.2.5 and the VAXC$ESTABLISH function in this section for more information.
Note
There are Alpha specific, non-standard decc$setjmp and decc$fast_longjmp functions. To use these non-standard functions instead of the standard ones, a program must be compiled with __FAST_SETJMP or __UNIX_SETJMP macros defined.
Unlike the standard longjmp function, the decc$fast_longjmp function does not convert its second argument from 0 to 1. After a call to decc$fast_longjmp , a corresponding setjmp function returns with the exact value of the second argument specified in the decc$fast_longjmp call.
You cannot invoke the longjmp function from an OpenVMS condition handler. However, you may invoke longjmp from a signal handler that has been established for any signal supported by the Compaq C RTL, subject to the following nesting restrictions:
- The longjmp function will not work if you invoke it from nested signal handlers. The result of the longjmp function, when invoked from a signal handler that has been entered as a result of an exception generated in another signal handler, is undefined.
- Do not invoke the setjmp function from a signal handler unless the associated longjmp is to be issued before the handling of that signal is completed.
- Do not invoke the longjmp function from within an exit handler (established with atexit or SYS$DCLEXH). Exit handlers are invoked after image tear-down, so the destination address of the longjmp no longer exists.
- Invoking longjmp from within a signal handler to return to the main thread of execution might leave your program in an inconsistent state. Possible side effects include the inability to perform I/O or to receive any more UNIX signals. Use siglongjmp instead.
See the Description section.
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