[英]Why doesn't this small C program work as expected?
I've got a small C program that makes use of difftime. 我有一个使用difftime的小型C程序。 its really strange, it doesn't print out the line after 10 seconds. 真的很奇怪,它在10秒后没有打印出来。
If however I uncomment out the sleep line then it works. 但是,如果我取消注释睡眠线,那么它将起作用。
Any ideas why this is happening? 任何想法为什么会这样?
/* difftime example */
#include <stdio.h> /* printf */
#include <time.h> /* time_t, struct tm, difftime, time, mktime */
int main ()
{
time_t start, stop;
start = time(NULL);
for(; /* some condition that takes forever to meet */;) {
// do stuff that apparently takes forever.
stop = time(NULL);
double diff = difftime(stop, start);
//sleep (1);
if (diff >= 10) {
printf("10 seconds passed...");
start = time(NULL);
}
}
}
BTW: Code compiles fine and I'm running it on the Raspberry Pi. 顺便说一句:代码可以很好地编译,我正在Raspberry Pi上运行它。 3.6.11+ #474 PREEMPT Thu Jun 13 17:14:42 BST 2013 armv6l GNU/Linux 3.6.11+#474 PREEMPT周四13月13日17:14:42 BST 2013 armv6l GNU / Linux
Console IO might be line buffered. 控制台IO可能是行缓冲的。 Try flushing 尝试冲洗
printf("10 seconds passed...");
fflush(stdout)
or adding a newline \\n
或添加换行符\\n
printf("10 seconds passed...\n");
I can't reproduce any change in behaviour when the call to sleep
is uncommented. 如果没有评论sleep
呼叫,我将无法重蹈覆辙。
printf("10 seconds passed...\n");
For sleep(), you need to include unistd.h, as well as adding a newline as others have pointed out. 对于sleep(),您需要包含unistd.h,并添加其他人指出的换行符。
#include <stdio.h> /* printf */
#include <time.h> /* time_t, struct tm, difftime, time, mktime */
#include <unistd.h> /* sleep() */
If your code compiled without warnings and without including unistd.h, you need to crank your warnings up. 如果您的代码编译时没有警告,也没有包含unistd.h,则需要提高警告程度。
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