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Two separate file descriptors are used for reading from and writing to the pipe, but only one mailbox is used so some I/O synchronization is required. For example, assume that the parent writes a message to the pipe. If the parent is the first process to read from the pipe, then it will read its own message back as shown in Figure REF-1.
Figure REF-1 Reading and Writing to a Pipe
0 Indicates success. --1 Indicates an error.
Initiates a pipe to a process.
#include <stdio.h>FILE *popen (const char *command, const char *type);
command
A pointer to a null-terminated string containing a shell command line.type
A pointer to a null-terminated string containing an I/O mode. Because open files are shared, you can use a type r command as an input filter and a type w command as an output filter. Specify one of the following values for the type argument:
- r -- the calling program can read from the standard output of the command by reading from the returned file stream.
- w -- the calling program can write to the standard input of the command by writing to the returned file stream.
This function creates a pipe between the calling program and a shell command awaiting execution. It returns a pointer to a FILE structure for the stream.
See also fflush , pclose , and setvbuf in this section.
x A pointer to the FILE structure for the opened stream. NULL Indicates an error. Unable to create files or processes.
Returns the first argument raised to the power of the second argument.
#include <math.h>double pow (double base, double exp);
base
A value of type double that is to be raised to a power.exp
The exponent to which the power base is to be raised.
Both arguments must be double and the returned value is double .
x The result of the first argument raised to the power of the second. 1.0 Indicates that the base is zero and the exponent is zero. HUGE_VAL Indicates that the result overflowed; errno is set to ERANGE. --HUGE_VAL Indicates that the base is zero and the exponent is negative; errno is set to EDOM.
#include <stdio.h> #include <math.h> #include <errno.h> main() { double x; errno = 0; x = pow(-3.0, 2.0); printf("%d, %f\n", errno, x); }This example program outputs the following:
0, 9.000000
Performs formatted output from the standard output (stdout). See Chapter 2 for information on format specifiers.
#include <stdio.h>int printf (const char *format_spec, ...);
format_spec
Characters to be written literally to the output or converted as specified in the ... arguments....
Optional expressions whose resultant types correspond to conversion specifications given in the format specification.If no conversion specifications are given, you may omit the output sources. Otherwise, the function call 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. Excess output pointers, if any, are ignored.
x The number of bytes written. Negative value Indicates that an output error occurred. The function sets errno . For a list of errno values set by this function, see fprintf in this section.
Perform a printf in the specified window, starting at the current position of the cursor. The printw function acts on the stdscr window.
#include <curses.h>printw (char *format_spec, ...);
int wprintw (WINDOW *win, char *format_spec, ...);
win
A pointer to the window.format_spec
A pointer to the format specification string....
Optional expressions whose resultant types correspond to conversion specifications given in the format specification.If no conversion specifications are given, you may omit the output sources. Otherwise, the function call 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. Excess output pointers, if any, are ignored.
The formatting specification (format_spec) and the other arguments are identical to those used with the printf function.The printw and wprintw functions format and then print the resultant string to the window using the addstr function. For more information, see the printf and scrollok functions in this section. See Chapter 2 for information on format specifiers.
OK Indicates success. ERR Indicates that the function makes the window scroll illegally.
The putc macro writes a single character to a specified file.
#include <stdio.h>int putc (int character, FILE *file_ptr);
character
An object of type int .file_ptr
A file pointer.
Since putc is a macro, a file pointer argument with side effects (for example, putc (ch, *f++) ) might be evaluated incorrectly. In such a case, use the fputc function instead. See also fputc in this section.
x The character written to the file. Indicates success. EOF Indicates output errors.
Writes a single character to the standard output (stdout) and returns the character.
#include <stdio.h>int putchar (int character);
character
An object of type int .
This function is identical to fputc (character, stdout).
character Indicates success. EOF Indicates output errors.
Sets an environmental variable.
#include <stdlib.h>int putenv (const char *string);
string
A pointer to a name=value string.
This function sets the value of an environment variable by altering an existing variable or by creating a new one. The string argument points to a string of the form name=value, where name is the environment variable and value is the new value for it.The string pointed to by string becomes part of the environment, so altering the string changes the environment. When a new string-defining name is passed to putenv , the space used by string is no longer used.
0 Indicates success. --1 Indicates an error. errno is set to ENOMEM---Not enough memory available to expand the environment list.
This function cannot take a 64-bit address. See Section 1.8.
Writes a character string to the standard output (stdout) followed by a new-line character.
#include <stdio.h>int puts (const char *str);
str
A pointer to a character string.
This function does not copy the terminating null character to the output stream.
Nonnegative value Indicates success. EOF Indicates output errors.
Writes characters to a specified file.
#include <stdio.h>int putw (int integer, FILE *file_ptr);
integer
An object of type int or long .file_ptr
A file pointer.
This function writes four characters to the output file as an int . No conversion is performed.
integer Indicates success. EOF Indicates output errors.
Converts a wide character to its corresponding multibyte value, and writes the result to a specified file.
#include <wchar.h>wint_t putwc (wint_t wc, FILE *file_ptr);
wc
An object of type wint_t .file_ptr
A file pointer.
Since putwc might be implemented as a macro, a file pointer argument with side effects (for example putwc (wc, *f++) ) might be evaluated incorrectly. In such a case, use the fputwc function instead. See also fputwc in this section.
x The character written to the file. Indicates success. WEOF Indicates an output error. The function sets errno . For a list of the errno values set by this function, see fputwc in this section.
Writes a wide character to the standard output (stdout) and returns the character.
#include <wchar.h>wint_t putwchar (wint_t wc);
wc
An object of type wint_t .
This function is identical to fputwc (wc, stdout).
x The character written to the file. Indicates success. WEOF Indicates an output error. The function sets errno . For a list of the errno values set by this function, see fputwc in this section.
Returns the absolute value of an integer as an __int64 . llabs is a synonym for qabs .
#include <stdlib.h>__int64 qabs (__int64 j);
__int64 llabs (__int64 j);
j
A value of type __int64 .
Returns the quotient and the remainder after the division of its arguments. lldiv is a synonym for qdiv .
#include <stdlib.h>qdiv_t qdiv (__int64 numer, __int64 denom);
lldiv_t lldiv (__int64 numer, __int64 denom);
numer
A numerator of type __int64 .denom
A denominator of type __int64 .
The types qdiv_t and lldiv_t are defined in the <stdlib.h> header file as follows:
typedef struct { __int64 quot, rem; } qdiv_t, lldiv_t;
Sorts an array of objects in place. It implements the quick-sort algorithm.
#include <stdlib.h>Function Variants This function also has variants named _qsort32 and _qsort64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.8 for more information on using pointer-size-specific functions.void qsort (void *base, size_t nmemb, size_t size, int (*compar) (const void *, const void *));
base
A pointer to the first member of the array. The pointer should be of type pointer-to-element and cast to type pointer-to-character.nmemb
The number of objects in the array.size
The size of an object, in bytes.compar
A pointer to the comparison function.
Two arguments are passed to the comparison function pointed to by compar. The two arguments point to the objects being compared. Depending on whether the first argument is less than, equal to, or greater than the second argument, the comparison function returns an integer less then, equal to, or greater than 0.The comparison function compar need not compare every byte, so arbitrary data might be contained in the objects in addition to the values being compared.
The order in the output of two objects that compare as equal is unpredictable.
Generates a specified software signal. Generating a signal causes the action routine established by the signal , ssignal , or sigvec function to be invoked.
#include <signal.h>int raise (int sig); (ANSI C)
int raise (int sig[, int sigcode]); (DEC C EXTENSION)
sig
The signal to be generated.sigcode
An optional signal code, available only when not compiling in strict ANSI C mode. For example, signal SIGFPE---the arithmetic trap signal---has 10 different codes, each representing a different type of arithmetic trap.The signal codes can be represented by mnemonics or numbers. The arithmetic trap codes are represented by the numbers 1 to 10; the SIGILL codes are represented by the numbers 0 to 2. The code values are defined in the <signal.h> header file. See Tables 4-4 and 4-5 for a list of signal mnemonics, codes, and corresponding OpenVMS exceptions.
Calling this function has one of the following results:
- If raise specifies a sig argument that is outside the range defined in the <signal.h> header file, then the raise function returns 0, and the errno variable is set to EINVAL.
- If signal , ssignal , or sigvec establishes SIG_DFL (default action) for the signal, then the functions do not return. The image is exited with the OpenVMS error code corresponding to the signal.
- If signal , ssignal , or sigvec establishes SIG_IGN (ignore signal) as the action for the signal, then raise returns its argument, sig.
- signal , ssignal , or sigvec must establish an action function for the signal. That function is called and its return value is returned by raise .
See Chapter 4 for more information on signal processing. See also gsignal , signal , ssignal , and sigvec in this section.
0 If successful. nonzero If unsuccessful.
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