在C

Question

我对C中的分叉过程有疑问。我理解这段代码：

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>

#define NP 5

int main()
{
    pid_t pid;

    for(int i=0;i<NP;i++) // loop will run n times (n=5)
    {

        pid = fork();

        if (pid) {
        printf("[PARENT] pid %d \n",getpid());
        }

        else if(pid == 0)
        {
            printf("[SON] pid %d from [PARENT] pid %d\n",getpid(),getppid());
            exit(0);
            //break;
        }

        else {
            printf("fork error\n");
            exit(1);
        }


    }

    for(int i=0;i<NP;i++) { // loop will run n times (n=5)
        wait(NULL);
        printf("Finish waiting for a process \n");
    }

    return 0;
}

输出：

./forkexample

[PARENT] pid 5377 
[PARENT] pid 5377 
[SON] pid 5378 from [PARENT] pid 5377
[PARENT] pid 5377 
[PARENT] pid 5377 
[SON] pid 5381 from [PARENT] pid 5377
[PARENT] pid 5377 
[SON] pid 5379 from [PARENT] pid 5377
Finish waiting for a process 
[SON] pid 5380 from [PARENT] pid 5377
Finish waiting for a process 
Finish waiting for a process 
Finish waiting for a process 
[SON] pid 5382 from [PARENT] pid 5377
Finish waiting for a process

我理解fork是如何工作的，孩子在fork之后开始行。 fork（）为子节点返回0。孩子进入pid == 0区块并中断/退出for循环。

但现在在这种情况下我需要为文件中的每一行（list.txt）分叉一个进程。我的list.txt有3行：001.txt，002.txt，003.txt（数据文件夹中包含3个文件的每个文件一个）。我的代码：

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>

#define MAXBUFFER  50

int main(int argc, char **argv)
{

    printf("--beginning of program\n");

    //write a C program that takes as arguments a number C and a directory name dir

    char buffer[MAXBUFFER];

    if(argc !=3) {
        printf("Error: two integers needed. c and directory  \n");
        return 0;
    }

    int c = atoi (argv[1]);

    printf("c: %d \n", c);
    printf("directory: %s \n", argv[2]);

    //The main program, using the system call system, outputs in a file list.txt the list of files in
    //directory dir.

    sprintf(buffer, "cd %s && ls -p | grep -v / -> ../list.txt", argv[2]);
    printf("command to execute: %s \n", buffer);
    system(buffer);

    //Then it reads the content of the file list.txt, and for each read line (a filename)

    char buf[1000];

    FILE * ptr_file;

    ptr_file =fopen("list.txt","r");

    if (!ptr_file)
        return 1;

    int nump = 0;

    printf("The parent MAIN process id: %d\n", getpid());

    pid_t  pid;


    while (fgets(buf,1000, ptr_file)!=NULL) {

        /* fgets: If a newline is read, it is stored into the buffer. 
            int len=strlen(buf);
            if(buf[len-1]=='\n') {
                buf[len-1]='\0';
        }*/

        pid = fork();

        if (pid) {
        printf("[PARENT] pid %d \n",getpid());
        }

        else if(pid == 0)
        {
            printf("[SON] pid %d from [PARENT] pid %d\n",getpid(),getppid());
            exit(0);
            //break;
        }

        else {
            printf("fork error\n");
            exit(1);
        }   
    }


    printf("Out of while. I'm process: %d \n - number of lines: %d", getpid(), nump);

    printf("--end of program--\n");

    return 0;
}

输出是这样的：

./es02 2 data
--beginning of program
c: 2 
directory: data 
command to execute: cd data && ls -p | grep -v / -> ../list.txt 
The parent MAIN process id: 5936
[PARENT] pid 5936 
[SON] pid 5941 from [PARENT] pid 5936
[PARENT] pid 5936 
[SON] pid 5942 from [PARENT] pid 5936
[PARENT] pid 5936 
[PARENT] pid 5936 
[SON] pid 5944 from [PARENT] pid 5936
[PARENT] pid 5936 
[PARENT] pid 5936 
[SON] pid 5945 from [PARENT] pid 5936
[PARENT] pid 5936 
Out of while. I'm process: 5936 
 - number of lines: 0--end of program--
[SON] pid 5946 from [PARENT] pid 5936
[SON] pid 5943 from [PARENT] pid 1
[SON] pid 5947 from [PARENT] pid 1

所以，我希望找到像上一个例子一样的三个过程，但是，有三个以上，因为孩子进入区块并退出。此外，我知道我暂时没有等待，但我认为这不会影响循环的行为。

我没有问如何解决问题，只是为什么循环因不创建3个子进程而表现不同。非常感谢你