linux下写文件write问题
小弟的一个工程，最后发现写文件写不进去，我写了一个小测试程序，能返回write成功写成功，可是文件里面还是空的
附代码
#include <stdio.h>
#include <string.h>
#include <fcntl.h> //文件操作相关头文件
#include <unistd.h>


int main()
{
char *msg="hello\0";

int filefd;
int wrflag=0;

if(filefd = open("tmp.txt",O_CREAT|O_RDWR) < 0)
{
printf("creat file is err!\n");
return 0;
}

wrflag = write(filefd,msg,sizeof(msg));
flush(filefd);
printf("wrflag is %d\n",wrflag);
return 0;
}
write成功却无现象
[解决办法]
WRITE
Section: Linux Programmer's Manual (2)
Updated: 2001-12-13
--------------------------------------------

NAME
write - write to a file descriptor
SYNOPSIS
#include <unistd.h>
ssize_t write(int fd, const void *buf, size_t count);

DESCRIPTION
write writes up to count bytes to the file referenced by the file descriptor fd from the buffer starting at buf. POSIX requires that a read() which can be proved to occur after a write() has returned returns the new data. Note that not all file systems are POSIX conforming.
RETURN VALUE
On success, the number of bytes written are returned (zero indicates nothing was written). On error, -1 is returned, and errno is set appropriately. If count is zero and the file descriptor refers to a regular file, 0 will be returned without causing any other effect. For a special file, the results are not portable.
ERRORS
EAGAIN
Non-blocking I/O has been selected using O_NONBLOCK and the write would block.
EBADF
fd is not a valid file descriptor or is not open for writing.
EFAULT
buf is outside your accessible address space.
EFBIG
An attempt was made to write a file that exceeds the implementation-defined maximum file size or the process' file size limit, or to write at a position past than the maximum allowed offset.

EINTR
The call was interrupted by a signal before any data was written.
EINVAL
fd is attached to an object which is unsuitable for writing.
EIO
A low-level I/O error occurred while modifying the inode.
ENOSPC
The device containing the file referred to by fd has no room for the data.
EPIPE
fd is connected to a pipe or socket whose reading end is closed. When this happens the writing process will also receive a SIGPIPE signal. (Thus, the write return value is seen only if the program catches, blocks or ignores this signal.)
Other errors may occur, depending on the object connected to fd.

CONFORMING TO
SVr4, SVID, POSIX, X/OPEN, 4.3BSD. SVr4 documents additional error conditions EDEADLK, ENOLCK, ENOLNK, ENOSR, ENXIO, or ERANGE. Under SVr4 a write may be interrupted and return EINTR at any point, not just before any data is written.
NOTES
A successful return from write does not make any guarantee that data has been committed to disk. In fact, on some buggy implementations, it does not even guarantee that space has successfully been reserved for the data. The only way to be sure is to call fsync(2) after you are done writing all your data.
SEE ALSO
close(2), fcntl(2), fsync(2), ioctl(2), lseek(2), open(2), read(2), select(2), fwrite(3), writev(3)
--------------------------------------------

[解决办法]
#include <stdio.h>
#include <string.h>
#include <fcntl.h> //文件操作相关头文件
#include <unistd.h>


int main()
{
char msg[]="hello";

int filefd;
int wrflag=0;

if((filefd = open("tmp.txt",777)) < 0)

{
printf("creat file is err!\n");
return 0;
}

wrflag = write(filefd,msg,strlen(msg));
close(filefd);
printf("wrflag is %d\n",wrflag);
return 0;

}