睡眠（）執行全部一次，而當它被稱爲

Question

我試圖做一個簡單的測驗在Linux中，像這樣：

#include <stdio.h> 
#include <unistd.h> 

void main() 
{ 
    printf("Simple arithmetic\n"); 
    printf("5 * 7 + 4/2 = ?\n"); 
    sleep(3);      //wait for 3 seconds 
    printf("And the answer is"); 
    for(int i = 5; i > 0; i--){ //wait for another 5 seconds printing a '.' each second 
     sleep(1); 
     printf(" ."); 
    } 
    printf("\n%d!\n", 5*7+4/2);  //reveal the answer 
} 

問題是，這個輸出弗里斯特2級的printf的，然後等待8或秒左右，然後打印一切出這樣的：

>> Simple arithmetic 
>> 5 * 7 + 4/2 = ? 
>> // waits for 8 seconds instead of 3 
>> And the answer is..... 
>> 37! // prints everything out with no delay in-between 

爲什麼會出現這種情況，我能做些什麼來解決這個問題？謝謝您的幫助！

Answer 1

如果要立即輸出，則需要刷新。

#include <stdio.h> 
#include <stdlib.h> 
#include <unistd.h> 
void main() 
{ 
     printf("Simple arithmetic\n"); 
     printf("5 * 7 + 4/2 = ?\n"); 
     sleep(3);      //wait for 3 seconds 
     printf("And the answer is"); 
     for(int i = 5; i > 0; i--){ //wait for another 5 seconds printing a '.' each second 
       sleep(1); 
       printf(" ."); 
       fflush(stdout); // this line will do magic 
     } 
     printf("\n%d!\n", 5*7+4/2);  //reveal the answer 
}