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.\"     @(#)setbuf.3	6.10 (Berkeley) 6/29/91
.\"
.\" Converted for Linux, Mon Nov 29 14:55:24 1993, faith@cs.unc.edu
.\" Added section to BUGS, Sun Mar 12 22:28:33 MET 1995,
.\"                   Thomas.Koenig@ciw.uni-karlsruhe.de
.\" Correction,  Sun, 11 Apr 1999 15:55:18,
.\"     Martin Vicente <martin@netadmin.dgac.fr>
.\" Correction,  2000-03-03, Andreas Jaeger <aj@suse.de>
.\" Added return value for setvbuf, aeb, 
.\"
.TH SETBUF 3  2001-06-09 "Linux" "Linux Programmer's Manual"
.SH NAME
setbuf, setbuffer, setlinebuf, setvbuf \- 流緩衝操作
.SH "SYNOPSIS 總覽"
.na
.B #include <stdio.h>
.sp
.BI "void setbuf(FILE *" stream ", char *" buf );
.br
.BI "void setbuffer(FILE *" stream ", char *" buf ", size_t "  size );
.br
.BI "void setlinebuf(FILE *" stream );
.br
.BI "int setvbuf(FILE *" stream ", char *" buf ", int " mode
.BI ", size_t " size );
.ad
.SH "DESCRIPTION 描述"
有三種類型的緩衝策略，它們是無緩衝，塊緩衝和行緩衝。當輸出流無緩衝時，信息在寫的同時出現於目標文件或終端上；當是塊緩衝時，字符被暫存，然後一起寫入；當是行緩衝時，字符被暫存，直到要輸出一個新行符，或者從任何與終端設備連接的流中 (典型的是 stdin) 讀取輸入時才輸出。函數
.BR fflush (3)
可以用來強制提前輸出。(參見
.BR fclose (3))
通常所有文件都是塊緩衝的。當文件 I/O 操作在文件上發生時，將調用
.BR malloc (3)
，獲得一個緩衝。如果流指向一個終端 (通常
.I stdout
都是這樣)，那麼它是行緩衝的。標準錯誤流
.I stderr
默認總是無緩衝的。
.PP
函數
.B setvbuf
可以用在任何打開的流上，改變它的緩衝。參數
.I mode
必須是下列三個宏之一：
.RS
.TP
.B _IONBF
無緩衝
.TP
.B _IOLBF
行緩衝
.TP
.B _IOFBF
完全緩衝
.RE
.PP
除非是無緩衝的文件，否則參數
.I buf
應當指向一個長度至少爲
.I size
字節的緩衝；這個緩衝將取代當前的緩衝。如果參數
.I buf
是
.BR NULL
，只有這個模式會受到影響；下次 read 或 write 操作還將分配一個新的緩衝。函數
.B setvbuf
只能在打開一個流，還未對它進行任何其他操作之前使用。
.PP
其他三個函數調用是函數
.BR setvbuf
的別名，函數
.B setbuf
與使用下列語句完全等價：
.PP
.RS
setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);
.RE
.PP
函數
.B setbuffer
與此相同，但是緩衝的長度由用戶決定，而不是由默認值
.BR BUFSIZ
決定。函數
.B setlinebuf
與使用下列語句完全等價：
.PP
.RS
setvbuf(stream, (char *)NULL, _IOLBF, 0);
.RE
.SH "RETURN VALUE 返回值"
函數
.B setvbuf
成功執行時返回 0。它失敗時可能返回任何值，但是當
It can return any value on failure, but returns nonzero when
.I mode
不正確，或者不能實現請求時，必須返回非零值。它在失敗時可能設置
.I errno
。其他函數沒有返回值。
.SH "CONFORMING TO 標準參考"
函數
.B setbuf
和
.B setvbuf
遵循 ANSI X3.159-1989 (``ANSI C'') 標準。
.SH BUGS
函數
.B setbuffer
和
.B setlinebuf
無法移植到 4.2BSD 之前的 BSD 版本，在 Linux 中僅在 libc 4.5.21 之後的系統中可用。在 4.2BSD 和 4.3BSD 系統中，
.B setbuf
總是使用非最優的緩衝大小，應當避免使用它。
.P
在
.I stream
被關閉時，必須確保
.I buf
和它指向的空間仍然存在。這通常發生在程序終止時。
.P
例如，下列調用是非法的：
.nf
.sp
#include <stdio.h>
int main()
{
    char buf[BUFSIZ];
    setbuf(stdin, buf);
    printf("Hello, world!\\n");
    return 0;
}
.fi
.sp
.SH "SEE ALSO 參見"
.BR fclose (3),
.BR fflush (3),
.BR fopen (3),
.BR fread (3),
.BR malloc (3),
.BR printf (3),
.BR puts (3)
.SH "跋"
.br
本頁面中文版由中文 man 手冊頁計劃提供。
.br
中文 man 手冊頁計劃：\fBhttps://github.com/man-pages-zh/manpages-zh\fR