Q5.1 Implement setbuf using setvbuf.
Q5.2 Type in the program that copies a file using line-at-a-time I/O (fgets and fputs) from Figure 5.5, but use a MAXLINE of 4. What happens if you copy lines that exceed this length?
Explain what is happening.
正常情況下，在stdin 輸入字符數小於4096時，我只顯示一行 hello this is a test.
但當我改爲4自後，fgets每到4個字符就重新執行一次fgets.
正常情況下
$ ./fgets
hello
hello thi sis a test
zhangbo
hello thi sis a test
改過自後 MAXLINE1 = 4 可以看到輸入兩個字符時沒有關係，fgets 運行一次。
當我輸入6個字符時它運行3次。
$ ./fgets
ldsakfjlsdk
hello thi sis a test
hello thi sis a test
hello thi sis a test
hello thi sis a test
sfdfds
hello thi sis a test
hello thi sis a test
hello thi sis a test
sd
hello thi sis a test
sdf
hello thi sis a test
hello thi sis a test
sd
hello thi sis a test
源代碼
$ cat fgets.c
#include "apue.h"
#define MAXLINE1 4
int
main (void)
{
char buf[MAXLINE1];
while ( fgets(buf, MAXLINE1, stdin) != NULL)
printf("hello thi sis a test\n");
if( fputs(buf, stdout) == EOF )
err_sys("output error");
if ( ferror(stdin))
err_sys("input error");
exit(0);
}
Q5.3 What does a return value of 0 from printf mean?
打印空的 printf(" ");
Q5.4 The following code works correctly on some machines, but not on others, What could be the problem?
#include <stdio.h>
int
main(void)
{
char c;
while (( c = getchar()) !== EOF)
putchar(c);
}
Q5.5 How would you use the fsync function(Section 3.13) with a standard I/O stream?
對於標準I/O流如何使用fsync函數？
The function fsync refers only to a single file, specified by the file descriptor fd, and waits for the disk writes to complete before returning, This function is used when an application, such as a database, needs to be sure that the modified blocks have been written to the disk.
with fsync, the file's attributes are also updated synchronously.
使用方法爲：先調用fflush，然後在調用fsync,fsync所使用的參數有fileno函數獲得。
如果不調用fflush,所有的數據仍然在內存緩衝區中，此時調用fsync將沒有任何效果。
Q5.6 In the programs in Figures 1.7 and 1.10, the prompt that is printed does not contain a newline, and we don't call fflush. What causes the prompt to be output?
在交互式設備中，標準輸入和標準輸出都是行緩衝方式，每次調用fgets時標準輸出自動沖洗。
Q5.7 BSD-based systems provide a function called funopen that allows us to intercept read, write, seek, and close calls on a stream. Use this function to implement fmemopen for FreeBSD and Mac OS X.