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編寫程序創建進程樹如圖1和圖2所示，在每個進程中顯示當前進程識別碼和父進程識別碼。

1

#include<stdio.h>
int main()
{
    int p1, p2, p3;//b, c, d
    while((p1=fork()) == -1) ;
    if(p1 != 0)
    {
        printf("process a\'s pid is %d, a\'s ppid is %d\n", getpid(), getppid());
    } 
    else 
    {
        while((p2=fork()) == -1) ;
        if(p2 != 0)
        {
            printf("process b\'s pid is %d, b\'s ppid is %d\n", getpid(), getppid());
        }
        else
        {
            while((p3=fork()) == -1) ;
            if(p3 != 0)
            {
                printf("process c\'s pid is %d, c\'s ppid is %d\n", getpid(), getppid());
            }
            else
            {
                printf("process d\'s pid is %d, d\'s ppid is %d\n", getpid(), getppid());
            }
        }
    }
}

2

version 1

#include<stdio.h>
int main()
{
    int p1, p2, p3, p4;//b,c,d,e
    while((p1=fork()) == -1 || (p3=fork()) == -1) ;
    if(p1 > 0 && p3 > 0)
    {
        printf("process a\'s pid is %d, a\'s ppid is %d\n", getpid(), getppid());
    }
    else if(p1 > 0)
    {
        while((p2=fork()) == -1) ;
        if(p2 > 0)
        {
            printf("process b\'s pid is %d, b\'s ppid is %d\n", getpid(), getppid());
        }
        else
        {
            printf("process c\'s pid is %d, c\'s ppid is %d\n", getpid(), getppid());
        }
    }
    else if (p3 > 0)
    {
        while((p4=fork()) == -1) ;
        if(p4 > 0)
        {
            printf("process d\'s pid is %d, d\'s ppid is %d\n", getpid(), getppid());
        }
        else
        {
            printf("process e\'s pid is %d, e\'s ppid is %d\n", getpid(), getppid());
        }
    }
}

version 2

通過對fork返回的值是否為零，判斷是否是在新建立的子進程中。

#include <stdio.h>

int main() {
    int p_b, p_c, p_d, p_e;
    while((p_b=fork()) == -1) ;
    if(0 == p_b) {
        while((p_c=fork()) == -1) ;
        if(0 == p_c) {
            printf("process c\'s pid is %d, c\'s ppid is %d\n", getpid(), getppid());
        } else {
            printf("process b\'s pid is %d, b\'s ppid is %d\n", getpid(), getppid());
        }
    } else {
        while((p_d=fork()) == -1) ;
        if (0 == p_d) {
            while((p_e=fork()) == -1) ;
            if (0 == p_e) {
                printf("process e\'s pid is %d, e\'s ppid is %d\n", getpid(), getppid());
            } else {
                printf("process d\'s pid is %d, d\'s ppid is %d\n", getpid(), getppid());
            }
        } else {
            printf("process a\'s pid is %d, a\'s ppid is %d\n", getpid(), getppid());
        }
    }
}

運行結果：
process a's pid is 3412, a's ppid is 2987
process b's pid is 3413, b's ppid is 3412
process c's pid is 3415, c's ppid is 3413
process d's pid is 3414, d's ppid is 3412
process e's pid is 3416, e's ppid is 3414

相關鏈接：

1.進程管理
2.unistd.h
3.wait