Windows PowerShell command on Get-command stdio

Manual Pages for UNIX Operating System command usage for man stdio

Standard C Library Functions stdio(3C)

NAME

stdio - standard buffered input/output package

SYNOPSIS

#include

extern FILE *stdin; extern FILE *stdout; extern FILE *stderr;

DESCRIPTION

The standard I/O functions described in section 3C of this

manual constitute an efficient, user-level I/O buffering

scheme. The in-line macros getc() and putc() handle charac-

ters quickly. The macros getchar(3C) and putchar(3C), and

the higher-level routines fgetc(3C), fgets(3C), fprintf(3C),

fputc(3C), fputs(3C), fread(3C), fscanf(3C), fwrite(3C), gets(3C), getw(3C), printf(3C), puts(3C), putw(3C), and scanf(3C) all use or act as if they use getc() and putc(); they can be freely intermixed. A file with associated buffering is called a stream (see Intro(3)) and is declared to be a pointer to a defined type FILE. The fopen(3C) function creates certain descriptive data for a stream and returns a pointer to designate the stream in all further transactions. Normally, there are three open streams with constant pointers declared in the

header and associated with the standard open

files: stdin standard input file stdout standard output file stderr standard error file The following symbolic values in define the file

descriptors that will be associated with the C-language

stdin, stdout and stderr when the application is started:

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Standard C Library Functions stdio(3C)

STDIN_FILENO Standard input value 0 stdin

STDOUT_FILENO Standard output value 1 stdout

STDERR_FILENO Standard error value 2 stderr

The constant NULL designates a null pointer.

The integer-constant EOF is returned upon end-of-file or

error by most integer functions that deal with streams (see the individual descriptions for details). The integer constant BUFSIZ specifies the size of the buffers used by the particular implementation.

The integer constant FILENAME_MAX specifies the number of

bytes needed to hold the longest pathname of a file allowed

by the implementation. If the system does not impose a max-

imum limit, this value is the recommended size for a buffer intended to hold a file's pathname.

The integer constant FOPEN_MAX specifies the minimum number

of files that the implementation guarantees can be open simultaneously. Note that no more than 255 files may be opened using fopen(), and only file descriptors 0 through 255 can be used in a stream.

The functions and constants mentioned in the entries of sec-

tion 3S of this manual are declared in that header and need no further declaration. The constants and the following "functions" are implemented as macros (redeclaration of these names is perilous): getc(), getchar(), putc(), putchar(), ferror(3C), feof(3C), clearerr(3C), and fileno(3C). There are also function versions of getc(), getchar(), putc(), putchar(), ferror(), feof(), clearerr(), and fileno(). Output streams, with the exception of the standard error stream stderr, are by default buffered if the output refers

to a file and line-buffered if the output refers to a termi-

nal. The standard error output stream stderr is by default unbuffered, but use of freopen() (see fopen(3C)) will cause

it to become buffered or line-buffered. When an output

stream is unbuffered, information is queued for writing on the destination file or terminal as soon as written; when it is buffered, many characters are saved up and written as a

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Standard C Library Functions stdio(3C)

block. When it is line-buffered, each line of output is

queued for writing on the destination terminal as soon as

the line is completed (that is, as soon as a new-line char-

acter is written or terminal input is requested). The set-

buf() or setvbuf() functions (both described on the setbuf(3C) manual page) may be used to change the stream's buffering strategy.

Interactions of Other FILE-Type C Functions

A single open file description can be accessed both through streams and through file descriptors. Either a file descriptor or a stream will be called a handle on the open

file description to which it refers; an open file descrip-

tion may have several handles. Handles can be created or destroyed by user action without affecting the underlying open file description. Some of the ways to create them include fcntl(2), dup(2), fdopen(3C), fileno(3C) and fork(2) (which duplicates existing ones into new processes). They can be destroyed by at least fclose(3C) and close(2), and by the exec functions (see exec(2)), which close some file descriptors and destroy streams. A file descriptor that is never used in an operation and could affect the file offset (for example read(2), write(2), or lseek(2)) is not considered a handle in this discussion, but could give rise to one (as a consequence of fdopen(), dup(), or fork(), for example). This exception does include the file descriptor underlying a stream, whether created with fopen() or fdopen(), as long as it is not used directly by the application to affect the file offset. (The read() and write() functions implicitly affect the file offset; lseek() explicitly affects it.) If two or more handles are used, and any one of them is a stream, their actions shall be coordinated as described below. If this is not done, the result is undefined. A handle that is a stream is considered to be closed when either an fclose() or freopen(3C) is executed on it (the result of freopen() is a new stream for this discussion, which cannot be a handle on the same open file description as its previous value) or when the process owning that

stream terminates the exit(2) or abort(3C). A file descrip-

tor is closed by close(), _exit() (see exit(2)), or by one

of the exec functions when FD_CLOEXEC is set on that file

descriptor.

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Standard C Library Functions stdio(3C)

For a handle to become the active handle, the actions below must be performed between the last other user of the first handle (the current active handle) and the first other user of the second handle (the future active handle). The second handle then becomes the active handle. All activity by the application affecting the file offset on the first handle shall be suspended until it again becomes the active handle. (If a stream function has as an underlying function that

affects the file offset, the stream function will be con-

sidered to affect the file offset. The underlying functions are described below.) The handles need not be in the same process for these rules to apply. Note that after a fork(), two handles exist where one existed before. The application shall assure that, if both handles will ever be accessed, that they will both be in a state where the other could become the active handle first. The application shall prepare for a fork() exactly as if it were a change of active handle. (If the only action

performed by one of the processes is one of the exec func-

tions or _exit(), the handle is never accessed in that pro-

cess.)

1. For the first handle, the first applicable condi-

tion below shall apply. After the actions required below are taken, the handle may be closed if it is still open. a. If it is a file descriptor, no action is required. b. If the only further action to be performed on any handle to this open file description is to close it, no action need be taken. c. If it is a stream that is unbuffered, no action need be taken.

d. If it is a stream that is line-buffered and the

last character written to the stream was a new-

line (that is, as if a putc('\n') was the most recent operation on that stream), no action need be taken. e. If it is a stream that is open for writing or append (but not also open for reading), either an fflush(3C) shall occur or the stream shall be closed. f. If the stream is open for reading and it is at the end of the file ( feof(3C) is true), no

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Standard C Library Functions stdio(3C)

action need be taken. g. If the stream is open with a mode that allows

reading and the underlying open file descrip-

tion refers to a device that is capable of seeking, either an fflush() shall occur or the stream shall be closed. h. Otherwise, the result is undefined.

2. For the second handle: if any previous active han-

dle has called a function that explicitly changed the file offset, except as required above for the first handle, the application shall perform an lseek() or an fseek(3C) (as appropriate to the type of the handle) to an appropriate location. 3. If the active handle ceases to be accessible before the requirements on the first handle above have been met, the state of the open file description becomes undefined. This might occur, for example,

during a fork() or an _exit().

4. The exec functions shall be considered to make inaccessible all streams that are open at the time they are called, independent of what streams or

file descriptors may be available to the new pro-

cess image. 5. Implementation shall assure that an application, even one consisting of several processes, shall

yield correct results (no data is lost or dupli-

cated when writing, all data is written in order, except as requested by seeks) when the rules above are followed, regardless of the sequence of handles used. If the rules above are not followed, the

result is unspecified. When these rules are fol-

lowed, it is implementation defined whether, and under what conditions, all input is seen exactly once.

Use of stdio in Multithreaded Applications

All the stdio functions are safe unless they have the

_unlocked suffix. Each FILE pointer has its own lock to

guarantee that only one thread can access it. In the case that output needs to be synchronized, the lock for the FILE

pointer can be acquired before performing a series of stdio

operations. For example: FILE iop; flockfile(iop); fprintf(iop, "hello ");

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Standard C Library Functions stdio(3C)

fprintf(iop, "world); fputc(iop, 'a'); funlockfile(iop); will print everything out together, blocking other threads that might want to write to the same file between calls to fprintf(). An unlocked interface is available in case performace is an issue. For example: flockfile(iop); while (!feof(iop)) {

*c++ = getc_unlocked(iop);

} funlockfile(iop);

RETURN VALUES

Invalid stream pointers usually cause grave disorder, possi-

bly including program termination. Individual function descriptions describe the possible error conditions.

Manual Pages for UNIX Operating System command usage for man stdio

Standard C Library Functions stdio(3C)

NAME

stdio - standard buffered input/output package

SYNOPSIS

#include

DESCRIPTION

header and associated with the standard open

Standard C Library Functions stdio(3C)

The integer constant FILENAME_MAX specifies the number of

Standard C Library Functions stdio(3C)

Standard C Library Functions stdio(3C)

Standard C Library Functions stdio(3C)

Use of stdio in Multithreaded Applications

All the stdio functions are safe unless they have the

pointer can be acquired before performing a series of stdio

Standard C Library Functions stdio(3C)

RETURN VALUES

SEE ALSO