QNX是类unix系统。
在c语言编程过程中，往往会用到delay或者sleep延时函数。两者之间在使用上有一定的区别！！！
delay()是循环等待，该进程还在运行，占用处理器。
sleep()不同，它会被挂起，把处理器让给其他的进程。 sleep()参数指定暂停时间，单位是s
delay()参数指定暂停时间，单位是ms
usleep功能:
暂停执行。 语法: void usleep(int micro_seconds); 返回值: 无 函数种类: PHP 系统功能 内容说明：本函数可暂时使程序停止执行。参数 micro_seconds 为要暂停的毫秒数（微妙还是毫秒？）。 注意：这个函数不能工作在 Windows 操作系统中。参见：usleep() 与sleep()类似，用于延迟挂起进程。进程被挂起放到reday queue。
只是一般情况下，延迟时间数量级是秒的时候，尽可能使用sleep()函数。
且，此函数已被废除，可使用nanosleep。
如果延迟时间为几十毫秒，或者更小，尽可能使用usleep()函数。这样才能最佳的利用CPU时间 delay:
函数名: delay
功 能: 将程序的执行暂停一段时间(毫秒)
用 法: void delay(unsigned milliseconds);
程序例:
/* Emits a 440-Hz tone for 500 milliseconds */
#include<dos.h>
int main(void)
{
sound(440);
delay(500);
nosound();
return 0;
} 附：QNX下相关解释
delay()
Suspends a calling thread for a given length of time
Synopsis:
#include <unistd.h> unsigned int delay( unsigned int duration );
Arguments:
- duration
- The number of milliseconds for which to suspend the calling thread from execution.
Library:
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
Description:
The delay() function suspends the calling thread for duration milliseconds.
sleep()
Suspend a thread for a given length of time
Synopsis:
#include <unistd.h> unsigned int sleep( unsigned int seconds );
Arguments:
- seconds
- The number of realtime seconds that you want to suspend the thread for.
Library:
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
Description:
The sleep() function suspends the calling thread until the number of realtime seconds specified by the seconds argument have elapsed, or the thread receives a signal whose action is either to terminate the process or to call a signal handler. The suspension time may be greater than the requested amount, due to the nature of time measurement (see the Tick, Tock: Understanding the Neutrino Microkernel's Concept of Time chapter of the QNX Neutrino Programmer's Guide), or due to the scheduling of other, higher priority threads by the system.
Returns:
0 if the full time specified was completed; otherwise, the number of seconds unslept if interrupted by a signal.
Examples:
/*
* The following program sleeps for the
* number of seconds specified in argv[1].
*/
#include <stdlib.h>
#include <unistd.h> int main( int argc, char **argv )
{
unsigned seconds; seconds = (unsigned) strtol( argv[1], NULL, 0 );
sleep( seconds ); return EXIT_SUCCESS;
}