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Page 1023 SEE ALSO printf(3), sprintf(3), vsprintf(3), stdarg(3) GNU, 16 September 1995 sqrtsqrt—Square root function SYNOPSIS #include <math.h> double sqrt(double x); DESCRIPTION The sqrt() function returns the non-negative square root of x. It fails and sets errno to EDOM, if x is negative. ERRORS
CONFORMS TO SVID 3, POSIX, BSD 4.3, ISO 9899 SEE ALSO hypot(3) 21 June 1993 stdargstdarg—Variable argument lists SYNOPSIS #include <stdarg.h> void va_start( va_list ap, last); type va_arg( va_list ap, type); void va_end( va_list ap); DESCRIPTION A function may be called with a varying number of arguments of varying types. The include file stdarg.h declares a type va_list and defines three macros for stepping through a list of arguments whose number and types are not known to the called function. The called function must declare an object of type va_list that is used by the macros va_start, va_arg, and va_end. The va_start macro initializes ap for subsequent use by va_arg and va_end, and must be called first. The parameter last is the name of the last parameter before the variable argument list; that is, the last parameter of which the calling function knows the type. Because the address of this parameter is used in the va_start macro, it should not be declared as a register variable, a function, or an array type. The va_start macro returns no value. Page 1024 The va_arg macro expands to an expression that has the type and value of the next argument in the call. The parameter ap is the va_list ap initialized by va_start. Each call to va_arg modifies ap so that the next call returns the next argument. The parameter type is a type name specified so that the type of a pointer to an object that has the specified type can be obtained simply by adding a * to type. If there is no next argument, or if type is not compatible with the type of the actual next argument (as promoted according to the default argument promotions), random errors will occur. The first use of the va_arg macro after that of the va_start macro returns the argument after last. Successive invocations return the values of the remaining arguments. The va_end macro handles a normal return from the function whose variable argument list was initialized by va_start. The va_end macro returns no value. EXAMPLE The function foo takes a string of format characters and prints out the argument associated with each format character based on the type.
void foo(char *fmt, ...)
{
va_list ap;
int d;
char c, *p, *s;
va_start(ap, fmt);
while (*fmt)
switch(*fmt++) {
case `s': /* string */
s = va_arg(ap, char *);
printf("string %s\n", s);
break;
case `d': /* int */
d = va_arg(ap, int);
printf("int %d\n", d);
break;
case `c': /* char */
c = va_arg(ap, char);
printf("char %c\n", c);
break;
}
va_end(ap);
}
STANDARDS The va_start, va_arg, and va_end macros conform to ANSI C3.159-1989 (ANSI C). COMPATIBILITY These macros are not compatible with the historic macros they replace. A backwards-compatible version can be found in the include file varargs.h. BUGS Unlike the varargs macros, the stdarg macros do not permit programmers to code a function with no fixed arguments. This problem generates work mainly when converting varargs code to stdarg code, but it also creates difficulties for variadic functions that wish to pass all of their arguments on to a function that takes a va_list argument, such as vfprintf(3). BSD man page, 29 November 1993 Page 1025 stdiostdio—Standard input/output library functions SYNOPSIS #include <stdio.h> FILE *stdin; FILE *stdout; FILE *stderr; DESCRIPTION The standard I/O library provides a simple and efficient buffered stream I/O interface. Input and output is mapped into logical data streams and the physical I/O characteristics are concealed. The functions and macros are listed in this section; more information is available from the individual man pages. A stream is associated with an external file (which may be a physical device) by opening a file, which may involve creating a new file. Creating an existing file causes its former contents to be discarded. If a file can support positioning requests (such as a disk file, as opposed to a terminal), then a file position indicator associated with the stream is positioned at the start of the file (byte zero), unless the file is opened with append mode. If append mode is used, the position indicator will be placed the end-of-file. The position indicator is maintained by subsequent reads, writes, and positioning requests. All input occurs as if the characters were read by successive calls to the fgetc(3) function; all output takes place as if all characters were read by successive calls to the fputc(3) function. A file is disassociated from a stream by closing the file. Output streams are flushed (any unwritten buffer contents are transferred to the host environment) before the stream is disassociated from the file. The value of a pointer to a FILE object is indeterminate after a file is closed (garbage). A file may be subsequently reopened, by the same or another program execution, and its contents reclaimed or modified (if it can be repositioned at the start). If the main function returns to its original caller, or the exit(3) function is called, all open files are closed (hence all output streams are flushed) before program termination. Other methods of program termination, such as abort(3) do not bother about closing files properly. At program startup, three text streams are predefined and need not be opened explicitly: standard input (for reading conventional input), standard output (for writing conventional input), and standard error (for writing diagnostic output). These streams are abbreviated stdin, stdout, and stderr. When opened, the standard error stream is not fully buffered; the standard input and output streams are fully buffered if and only if the streams do not to refer to an interactive device. Output streams that refer to terminal devices are always line buffered by default; pending output to such streams is written automatically whenever an input stream that refers to a terminal device is read. In cases where a large amount of computation is done after printing part of a line on an output terminal, it is necessary to fflush(3) the standard output before going off and computing so that the output will appear. The stdio library is a part of the library libc and routines are automatically loaded as needed by the compilers cc(1) and pc(1). The SYNOPSIS sections of the following manual pages indicate which include files are to be used, what the compiler declaration for the function looks like, and which external variables are of interest. The following are defined as macros; these names may not be reused without first removing their current definitions with #undef: BUFSIZ, EOF, FILENAME_MAX, FOPEN_MAX, L_cuserid, L_ctermid, L_tmpnam, NULL, SEEK_END, SEEK_SET, SEE_CUR, TMP_MAX, clearerr, feof, ferror, fileno, fropen, fwopen, getc, getchar, putc, putchar, stderr, stdin, stdout. Function versions of the macro functions feof, ferror, clearerr, fileno, getc, getchar, putc, and putchar exist and will be used if the macros definitions are explicitly removed. SEE ALSO open(2), close(2), read(2), write(2) |
