作者mikasamikoto (米卡莎美琴)
看板Grad-ProbAsk
標題[理工] [作業系統]課本fork問題
時間Sun Oct 23 11:49:41 2022
恐龍本題目
3.1 Using the program shown in Figure 3.30, explain what the output will be
at Line A.
Figure 3.30:
#include <sys/types.h>
#include <stdio.h>
#include <unistd.h>
int value = 5;
int main()
{
pid t pid;
pid = fork();
if (pid == 0) { /* child process */
value += 15;
return 0;
}
else if (pid > 0) { /* parent process */
wait(NULL);
printf("PARENT: value = %d",value); /* LINE A *
return 0;
}
}
解答:
Answer:
The result is still 5 as the child updates its copy of value. When control
returns to the parent, its value remains at 5.
奇怪有wait的時候父不是會等子做完嗎? 這樣value應該有更新成20了吧
感謝
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1F：推 KaryuuIssen: 如同解答寫的 子程序的變數會是副本 跟父程序不相干 10/23 13:03
2F：推 jemmy9211: data section 是分開的 10/23 15:57