阅读已经连续使用C打开的文件 [英] Reading already opened file continuously using C
问题描述
我实现低重量的应用程序在那里我有打开并经常阅读的/ proc / PID或TID /任务/ STAT细节。如果应用程序是多线程我要读更多的统计文件。所以打开,读取和关闭使我的监视应用程序很慢。是否有解决方案,以避免在打开文件多次,仍然能够读取更新的内容?
我跑了以下实验,但我没有看到成功。我更改了数据的test.txt,但新的数据不被读取。难道是因为文件没有在内存中更新?当我修改和保存的test.txt该怎么办?
的#include<&stdio.h中GT;
诠释的main()
{
FILE * PFILE;
焦了mystring [100];
PFILE = FOPEN(test.txt的,R);
而(1){
如果(PFILE == NULL)PERROR(错误打开文件);
如果(与fgets(MyString的,100,PFILE)!= NULL){
看跌期权(myString的);
fseek的(PFILE,0,SEEK_SET);
}
睡眠(1);
}
FCLOSE(PFILE);
返回0;
}
尝试是这样的:
为(;;){
而((CH = GETC(FP))!= EOF){
如果(的putchar(CH)== EOF)
PERROR(输出错误);
}
如果(FERROR(FP)){
的printf(输入错误:%s,错误号);
返回;
}
(无效)fflush(标准输出);
睡眠(1); //或者使用SELECT
}
您可以通过研究源$ C $找到一个完整的示例下尾。在$ C $上面c是forward.c修改的节选。
您可以使用选择
来监控新的数据几个文件(你需要保持通畅)。
I am implementing a low weight application where I have to open and read the /proc/pid or tid/task/stat details very often. If the application is multithreaded I have to read more stat files. So opening, reading and closing makes my monitoring application really slow. Is there a solution to avoid opening the file repeatedly and still able to read the updated content?
I ran the following experiment but I don't see success. I change the data in "test.txt" but the new data is not read. Is it because the file is not updated in memory? What happens when i modify and save "test.txt"?
#include <stdio.h>
int main()
{
FILE * pFile;
char mystring [100];
pFile = fopen ("test.txt" , "r");
while(1){
if (pFile == NULL) perror ("Error opening file");
if ( fgets (mystring , 100 , pFile) != NULL ){
puts (mystring);
fseek ( pFile , 0 , SEEK_SET );
}
sleep(1);
}
fclose (pFile);
return 0;
}
Try something like this:
for (;;) {
while ((ch = getc(fp)) != EOF) {
if (putchar(ch) == EOF)
perror("Output error");
}
if (ferror(fp)) {
printf("Input error: %s", errno);
return;
}
(void)fflush(stdout);
sleep(1); // Or use select
}
You can find a full example by studying the source code for tail. The code above is a modified excerpt from forward.c.
You can use select
to monitor several files for new data (you need to keep them open).
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