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Provides an interface to the dynamic library loader to allow shareable images to be loaded and called at run time.
#include <stdio.h>void *dlopen (char *pathname, int mode);
pathname
The name of the shareable image. This name is saved for subsequent use by the dlsym function.mode
This parameter is ignored on OpenVMS systems.
This function provides an interface to the dynamic library loader to allow shareable images to be loaded and called at run time.The dlopen function does not load a shareable image but rather saves its pathname argument for subsequent use by the dlsym function. dlsym is the function that actually loads the shareable image through a call to LIB$FIND_IMAGE_SYMBOL.
The pathname argument of the dlopen function must be the name of the shareable image. This name is passed as-is by the dlsym function to the LIB$FIND_IMAGE_SYMBOL routine as the filename argument. No image-name argument is specified in the call to LIB$FIND_IMAGE_SYMBOL, so default file specification of SYS$SHARE:.EXE is applied to the image name.
The dlopen function returns a handle that is used by a dlsym or dlclose call. If an error occurs, a NULL pointer is returned.
x A handle to be used by a dlsym or dlclose call. NULL Indicates an error.
Returns the address of the symbol name found in a shareable image.
#include <stdio.h>void *dlsym (void *handle, char *name);
handle
Pointer to the shareable image.
The dlsym function returns the address of the symbol name found in the shareable image corresponding to handle. If the symbol is not found, a NULL pointer is returned.
x Address of the symbol name found. NULL Indicates that the symbol was not found.
Generates uniformly distributed pseudorandom number sequences. Returns 48-bit, nonnegative, double-precision floating-point values.
#include <stdlib.h>double drand48 (void);
This function generates pseudorandom numbers using the linear congruential algorithm and 48-bit integer arithmetic.It returns non-negative, double-precision, floating-point values uniformly distributed over the range of y values such that 0.0 <= y < 1.0.
Before you call drand48 , use either srand48 , seed48 , or lcong48 to initialize the random number generator. You must initalize prior to invoking the drand48 function 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 drand48 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 lcong48 , the multiplier value a and the addend value c are:
a = 5DEECE66D16 = 2736731631558 c = B16 = 138The values returned by drand48 are 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 srand48 , seed48 , lcong48 , lrand48 , and mrand48 in this section.
n A nonnegative, double-precision, floating-point value.
Allocate a new descriptor that refers to a file specified by a file descriptor returned by open , creat , or pipe .
#include <unistd.h>int dup (int file_desc1);
int dup2 (int file_desc1, int file_desc2);
file_desc1
The file descriptor being duplicated.file_desc2
The new file descriptor to be assigned to the file designated by file_desc1.
The dup function causes a previously unallocated descriptor to refer to its argument, while the dup2 function causes its second argument to refer to the same file as its first argument.The argument file_desc1 is invalid if it does not describe an open file; file_desc2 is invalid if the new file descriptor cannot be allocated. If file_desc2 is connected to an open file, that file is closed.
n The new file descriptor. --1 Indicates that an invalid argument was passed to the function.
Set the terminal so that characters may or may not be echoed on the terminal screen. This mode of single-character input is only supported with Curses.
#include <curses.h>void echo (void);
void noecho (void);
The noecho function may be helpful when accepting input from the terminal screen with wgetch and wgetstr ; it prevents the input characters from being written onto the screen.
Converts its argument to a null-terminated string of ASCII digits and returns the address of the string. The string is stored in a thread-specific memory location created by the Compaq C RTL.
#include <stdlib.h>char *ecvt (double value, int ndigits, int *decpt, int *sign);
value
An object of type double that is converted to a null-terminated string of ASCII digits.ndigits
The number of ASCII digits to be used in the converted string.decpt
The position of the decimal point relative to the first character in the returned string. A negative int value means that the decimal point is decpt number of spaces to the left of the returned digits, (the spaces being filled with zeros). A 0 value means that the decimal point is immediately to the left of the first digit in the returned string.sign
An integer value that indicates whether the value argument is positive or negative. If value is negative, the function places a nonzero value at the address specified by sign. Otherwise, the function assigns 0 to the address specified by sign.
This function converts value to a null-terminated string of length ndigits, and returns a pointer to it. The resulting low-order digit is rounded to the correct digit for outputting ndigits digits in C E-format. The decpt argument is assigned the position of the decimal point relative to the first character in the string.Repeated calls to the ecvt function overwrite any existing string.
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 gcvt and fcvt in this section.
x The value of the converted string.
Clears the terminal screen and frees any virtual memory allocated to Curses data structures.
#include <curses.h>void endwin (void);
A program that calls Curses functions must call the endwin function before exiting to restore the previous environment of the terminal screen.
Generate uniformly distributed pseudorandom number sequences. Returns 48-bit nonnegative, double-precision, floating-point values.
#include <stdlib.h>double erand48 (unsigned short int xsubi[3]);
xsubi
An array of three short int , which form a 48-bit integer when concatentated together.
This function generates pseudorandom numbers using the linear congruential algorithm and 48-bit integer arithmetic.It returns nonnegative, double-precision, floating-point values uniformly distributed over the range of y values, such that, 0.0 <= y < 1.0.
The erand48 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 erand48 function requires that the calling program pass an array as the xsubi argument. For the first call, the array must be initialized to the value of the pseudorandom number sequence. Unlike the drand48 function, it is not necessary to call an initialization function prior to the first call.
By using different arguments, the erand48 function allows separate modules of a large program to generate several independent sequences of pseudorandom numbers; for example, the sequence of numbers that one module generates does not depend upon how many times the function is called by other modules.
n A nonnegative, double-precision, floating-point value.
Erase the window by painting it with blanks. The erase function acts on the stdscr window.
#include <curses.h>int erase();
int werase (WINDOW *win);
win
A pointer to the window.
Both the erase and werase functions leave the cursor at the current position on the terminal screen after completion; they do not return the cursor to the home coordinates of (0,0).
OK Indicates success. ERR Indicates an error.
Passes the name of an image to be activated in a child process. This function is nonreentrant.
#include <unistd.h>int execl (const char *file_spec, const char *arg0, ..., (char *)0); (ISO POSIX-1)
int execl (char *file_spec, ...); (COMPATABILITY)
file_spec
The full file specification of a new image to be activated in the child process.arg0, ...
A sequence of pointers to null-terminated character strings.If the POSIX-1 format is used, at least one argument must be present and must point to a string that is the same as the new process file name (or its last component). (This pointer can also be the NULL pointer, but then execle would accomplish nothing.) The last pointer must be the NULL pointer. This is also the convention if the compatibility format is used.
To understand how the exec functions operate, consider how the OpenVMS system calls any Compaq C program, as shown in the following syntax:
int main (int argc, char *argv[], char *envp[]);
The identifier argc is the argument count; argv is an array of argument strings. The first member of the array (argv[0]) contains the name of the image. The arguments are placed in subsequent elements of the array. The last element of the array is always the NULL pointer.
An exec function calls a child process in the same way that the run-time system calls any other Compaq C program. The exec functions pass the name of the image to be activated in the child; this value is placed in argv[0]. However, the functions differ in the way they pass arguments and environment information to the child:
- Arguments can be passed in separate character strings ( execl , execle , and execlp ) or in an array of character strings ( execv , execve , and execvp ).
- The environment can be explicitly passed in an array ( execle and execve ) or taken from the parent's environment ( execl , execv , execlp , and execvp ).
If vfork was called before invoking an exec function, then when the exec function completes, control is returned to the parent process at the point of the vfork call. If vfork was not called, the exec function waits until the child has completed execution and then exits the parent process. See vfork in this section and Chapter 5 for more information.
--1 Indicates failure.
Passes the name of an image to be activated in a child process. This function is nonreentrant.
#include <unistd.h>int execle (char *file_spec, char *arg0, ..., (char *)0, char *envp[]); (ISO POSIX-1)
int execle (char *file_spec, ...); (COMPATABILITY)
file_spec
The full file specification of a new image to be activated in the child process.arg0, ...
A sequence of pointers to null-terminated character strings.If the POSIX-1 format is used, at least one argument must be present and must point to a string that is the same as the new process file name (or its last component). (This pointer can also be the NULL pointer, but then execle would accomplish nothing.) The last pointer must be the NULL pointer. This is also the convention if the compatibility format is used.
envp
An array of strings that specifies the program's environment. Each string in envp has the following form:
name = value
The name can be one of the following names and the value is a null-terminated string to be associated with the name:
- HOME---Your login directory
- TERM---The type of terminal being used
- PATH---The default device and directory
- USER---The name of the user who initiated the process
The last element in envp must be the NULL pointer.
When the operating system executes the program, it places a copy of the current environment vector (envp) in the external variable environ.
See execl in this section for a description of how the exec functions operate.
--1 Indicates failure.
Passes the name of an image to be activated in a child process. This function is nonreentrant.
#include <unistd.h>int execlp (const char *file_name, const char *arg0, ..., (char *)0); (ISO POSIX-1)
int execlp (char *file_name, ...); (COMPATABILITY)
file_name
The file name of a new image to be activated in the child process. The device and directory specification for the file is obtained by searching the environment name VAXC$PATH.argn
A sequence of pointers to null-terminated character strings. By convention, at least one argument must be present and must point to a string that is the same as the new process file name (or its last component)....
A sequence of pointers to strings. At least one pointer must exist to terminate the list. This pointer must be the NULL pointer.
See execl in this section for a description of how the exec functions operate.
--1 Indicates failure.
Passes the name of an image to be activated in a child process. This function is nonreentrant.
#include <unistd.h>int execv (char *file_spec, char *argv[]);
file_spec
The full file specification of a new image to be activated in the child process.argv
An array of pointers to null-terminated character strings. These strings constitute the argument list available to the new process. By convention, argv[0] must point to a string that is the same as the new process file name (or its last component). argv is terminated by a NULL pointer.
See execl in this section for a description of how the exec functions operate.
--1 Indicates failure.
Passes the name of an image to be activated in a child process. This function is nonreentrant.
#include <unistd.h>int execve (const char *file_spec, char *argv[], char *envp[]);
file_spec
The full file specification of a new image to be activated in the child process.argv
An array of pointers to null-terminated character strings. These strings constitute the argument list available to the new process. By convention, argv[0] must point to a string that is the same as the new process file name (or its last component). argv is terminated by a NULL pointer.envp
An array of strings that specifies the program's environment. Each string in envp has the following form:
name = value
The name can be one of the following names and the value is a null-terminated string to be associated with the name:
- HOME---Your login directory
- TERM---The type of terminal being used
- PATH---The default device and directory
- USER---The name of the user who initiated the process
The last element in envp must be the NULL pointer.
When the operating system executes the program, it places a copy of the current environment vector (envp) in the external variable environ .
See execl in this section for a description of how the exec functions operate.
--1 Indicates failure.
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