我正在编写一些代码来管理 LittleFS 文件系统的文件时间(atime、ctime 和 mtime)。 在我想让这有点像 Linux/Posix 的过程中,我遇到了关于这些时间何时在生命周期中设置的问题。 当您打开文件、读取记录或关闭该文件时,诸如时间是否更新之类的问题。 为了回答这些问题,我启动了 WSL 子系统并编写了一个快速测试。 对结果感到非常惊讶,甚至质疑我对现实的把握。 在程序执行期间时间根本没有改变。 统计数据是否被缓存? 怎么才能刷新呢?
这是测试程序:
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <time.h>
#include <unistd.h>
char* mytime(const time_t *timep)
{
struct tm *tm = localtime(timep);
static char text[20];
sprintf(text, "%d:%02d:%02d", tm->tm_hour, tm->tm_min, tm->tm_sec);
return text;
}
void test_stat(const char *filename)
{
printf("Stat of %s ", filename);
struct stat statbuf = { 0 };
int rc = stat(filename, &statbuf);
if (rc != 0)
{
printf("stat rc=%d, errno=%d, %s\n", rc, errno, strerror(errno));
return;
}
printf("st_atime=%s, st_ctime=%s, st_mtime=%s\n",
mytime(&statbuf.st_atime),
mytime(&statbuf.st_ctime), mytime(&statbuf.st_mtime));
}
int main(int argc, char *argv)
{
static const char *filename = "testfile";
static int perm = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH;
test_stat(filename);
int fh = open(filename, 0, perm);
if (fh < 0)
{
printf("open rc=%d, errno=%d, %s\n", fh, errno, strerror(errno));
}
else
{
test_stat(filename);
}
printf("Open Create\n");
fh = open(filename, O_CREAT, perm);
if (fh < 0)
{
printf("open O_CREAT rc=%d, errno=%d, %s\n", fh, errno,
strerror(errno));
}
else
{
test_stat(filename);
}
printf("Write\n");
char *buffer = "1234567890";
write(fh, buffer, strlen(buffer));
test_stat(filename);
printf("Close fh=%d\n", fh);
int rc = close(fh);
if (rc < 0)
{
printf("close rc=%d, errno=%d, %s\n", rc, errno, strerror(errno));
}
sleep(2);
test_stat(filename);
sleep(2);
printf("Reopen, O_RDWR\n");
fh = open(filename, O_RDWR);
if (fh < 0)
{
printf("open rc=%d, errno=%d, %s\n", fh, errno, strerror(errno));
}
else
{
test_stat(filename);
}
printf("Write more\n");
write(fh, buffer, strlen(buffer));
test_stat(filename);
printf("Close\n");
rc = close(fh);
if (fh < 0)
{
printf("close rc=%d, errno=%d, %s\n", fh, errno, strerror(errno));
}
test_stat(filename);
sleep(2);
printf("Reopen, O_WRONLY\n");
fh = open(filename, O_WRONLY);
if (fh < 0)
{
printf("open rc=%d, errno=%d, %s\n", fh, errno, strerror(errno));
}
else
{
test_stat(filename);
}
printf("Write more\n");
write(fh, buffer, strlen(buffer));
test_stat(filename);
printf("Close\n");
rc = close(fh);
if (fh < 0)
{
printf("close rc=%d, errno=%d, %s\n", fh, errno, strerror(errno));
}
test_stat(filename);
sleep(2);
}
结果:
waynej@SV3273:~/testTimes$ rm -f testfile; cc -o testTimes testTimes.c && ./testTimes
Stat of testfile stat rc=-1, errno=2, No such file or directory
open rc=-1, errno=2, No such file or directory
Open Create
Stat of testfile st_atime=10:06:48, st_ctime=10:06:48, st_mtime=10:06:48
Write
Stat of testfile st_atime=10:06:48, st_ctime=10:06:48, st_mtime=10:06:48
Close fh=3
Stat of testfile st_atime=10:06:48, st_ctime=10:06:48, st_mtime=10:06:48
Reopen, O_RDWR
Stat of testfile st_atime=10:06:48, st_ctime=10:06:48, st_mtime=10:06:48
Write more
Stat of testfile st_atime=10:06:48, st_ctime=10:06:48, st_mtime=10:06:48
Close
Stat of testfile st_atime=10:06:48, st_ctime=10:06:48, st_mtime=10:06:48
Reopen, O_WRONLY
Stat of testfile st_atime=10:06:48, st_ctime=10:06:48, st_mtime=10:06:48
Write more
Stat of testfile st_atime=10:06:48, st_ctime=10:06:48, st_mtime=10:06:48
Close
Stat of testfile st_atime=10:06:48, st_ctime=10:06:48, st_mtime=10:06:48
printf("st_atime=%s, st_ctime=%s, st_mtime=%s\n",
mytime(&statbuf.st_atime),
mytime(&statbuf.st_ctime),
mytime(&statbuf.st_mtime));
现在向离您最近的橡皮鸭解释一下,当
printf
返回时,您期望 mytime
如何打印 三个不同的字符串
static char text[20];
每一次。
这就是你的问题。不要使用静态变量。他们会咬你。