使用等待从子进程检索返回代码（）？(Retrieving return code from chil

我有2个文件“prime.c”和“singlePrime.c”和singlePrime.c里面我想创建本身变身为“isPrime.exe”，这是做出来的“prime.c”可执行一个孩子。我想要做的就是从isPrime.exe得到回报号码，以便取决于如果输入的号码是质不是1或0，然后保存它childNum“singlePrime.c”的main（）函数的内部，从而我可以打印到终端它是否是一个素数或不基于1或0，其从“isPrime.exe”返回。下面是我的2个文件：

prime.c：

/*
File is isPrime.c

Purpose:
a program that checks if a given number is a prime number

input:
number - a positive int  entered via the command line parameters.  For example isPrime 1234

output:
0 - if the input number is not a prime number
1 - if the input number is a prime number
2 - if the command line parameter is not correct

Assumption:
the program does not check if the number is a positive integer

*/


#include "stdio.h"
#include "stdlib.h"
#include <unistd.h>
#include "prime.h"

int main(int argc, char *argv[])
{
        int i;

        int number;

        if (argc < 2) {
            printf("Returning 2");
            return(2);
        }
        else number = atoi(argv[1]);
        if (isPrime(number)) {
                exit(1);
        }
        exit(0);
}


/*
Purpose: check if the input number is a prime number
input:
number - the number to be checked

return:
0 - if the number is not a prime number
1 - if the number is a prime number
*/
int isPrime(int number)
{
        int i;
        for(i = 2; i*i < number; i++) {
                usleep(100);
                if (number % i == 0) {
                        printf("%d is not a prime number!",number);
                        return(0);
                }
        }
        printf("%d is a prime number!",number);
        return(1);
}

singlePrime.c：

#include "stdio.h"
#include "stdlib.h"
#include <unistd.h>
#include "prime.h"

int main(int argc, char *argv[])
{
        int number, childNum;

        if (!atoi(argv[1])) {
                printf("Please use a valid integer as an argument!");
                exit(1);
        }

        int pid = fork();

        if (pid == 0) {
                wait(childNum);
                morph(argv[1]);
        }

        else {
                if (childNum == 0) {
                        printf("The input number is not a prime number!");
                        exit(1);
                }
                else if (childNum == 1) {
                        printf("The input number is a prime number!");
                        exit(1);
                }
                else if (childNum == 2) {
                        printf("Please input a number greater than 2!");
                        exit(1);
                }
        }
}

void morph(char *number)
{
        char *primeArgv[] = {
                "isPrime.exe",
                number,
                NULL,
        };

        execvp("isPrime.exe",primeArgv);               
}

Answer 1:

对于初学者来说，这

wait(childNum);

应该让编译器发出明确警告，从中你可能会得出有什么不对。

事实上你正在使用wait()错误。它需要一个指向：

wait(int * status);

使用它的方式如下：

  {
    int status;
    int result;

    do
    {
      result = 0;
      if ((pid_t) -1) == wait(&status)))
      {
        result = -1;
        if (errno == EINTR)
        {
          continue;
        }
        else
        {
          perror("wait() failed");
        }
      }

      break;
    } while (1);

    if (-1 != result)
    {
      if (WIFEXITED(status))
      {
        int ec = WEXITSTATUS(status);
        printf("The child's exit code is %d\n", ec);
      }
      else
      {
        printf("The child did not provide an exit code. It probably crashed?\n");
      }
    }
  }

详情可读取的文档。

另外这个代码不知何故没有意义：

        if (pid == 0) {
            wait(childNum);
            morph(argv[1]);
        }

要调用wait()从孩子，只有经过它返回你exec* isPrime.exe 。

您可能需要像这样做

      pid = fork();
      if (-1 == pid)
      {
         perror("fork() failed");
      }
      else if (pid == 0) 
      {
        morph(argv[1]);
      }
      else
      {
        /* wait code as shown above goes here.
           childNum needs to get assigend. */
        if (childNum == 0) {
        ....
      }

此外^ 2的代码不测试呼叫是否execvp()成功了。

将一个perror("execvp() failed"); 在它的后面。

此外^ 3本