Printf语句不输出

Question

我对 C 还比较陌生，我目前正在尝试编写一个并发进程程序，但是每当我进入子进程时，它只打印出 Printf 语句的一部分，如下所示：

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

int concurrent(int num, int numOfProcs, int *nump)
{
  pid_t pid;

  pid = fork();
  if (pid < 0)
  {
    perror("There was an error during fork call: ");
    exit(1);
  }

  //child Processes
  if (pid == 0)
  {
    for (int i = 0; i < numOfProcs; i++)
    {
      printf("\nBEFORE Increment, ");
      printf(" \nChild number: %d",i);
      printf(" \nChild process ID: %d",(int) getpid());
      printf(" \nCurrent value of num: %d", num);
      printf(" \nCurrent value of nump: %d", *nump);
      printf(" \nCurrent value of x: %d", x);


      x += 5;
      num ++;
      *nump++;

      printf("\nAFTER Increment, ");
      printf(" \nChild number: %d",i);
      printf(" \nChild process ID: %d",(int) getpid());
      printf(" \nCurrent value of num: %d", num);
      printf(" \nCurrent value of nump: %d", *nump);
      printf(" \nCurrent value of x: %d", x);

    }
    exit(0);
  }
  //parent process
  else
  {
    for(int i = 0; i < numOfProcs; i++)
    {
      wait(NULL);
      printf("\nChild Process ended, Child PID: %d",(int) getpid());
    }

  }
}


int main (int argc, char *argv[])
{
  char *a = argv[1];
  int numOfProcs = atoi(a);
  x = 10;
  int num = 50;
  int *nump = malloc(100);
  *nump = 100;
  
  printf("\nCurrent Values");
  printf("\nNumber of processes: %d",numOfProcs);
  printf("\nCurrent value of num: %d", num);
  printf("\nCurrent value of nump: %d", *nump);
  printf("\nCurrent value of x: %d", x);

  concurrent(num,numOfProcs,&nump);

  exit(0);
}

这是现在的输出：

Current Values
Number of processes: 2
Current value of num: 50
Current value of nump: 100
Current value of x: 10
BEFORE Increment,  
Child number: 0 
Child process ID: 35148 
Current value of x: 10
Child Process ended, Child PID: 35147
Child Process ended, Child PID: 35147

我只是有点困惑为什么它不输出“AFTER Increment”和其余的打印语句，任何帮助将不胜感激。

Answer 1

使用

-Wall

构建二进制文件时会发现一些问题：

• x

  未初始化

• *nump++

  ：

  the value is not used

  （因为您增加了指针

  nump

  ，而不是它所指向的值 - 并且然后取消引用指针，请参阅运算符优先级）

这是修复后的代码：

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

int concurrent(int num, int numOfProcs, int *nump)
{
  pid_t pid;
  int x = 0;

  pid = fork();
  if (pid < 0)
  {
    perror("There was an error during fork call: ");
    exit(1);
  }

  //child Processes
  if (pid == 0)
  {
    for (int i = 0; i < numOfProcs; i++)
    {
      printf("\nBEFORE Increment, ");
      printf(" \nChild number: %d",i);
      printf(" \nChild process ID: %d",(int) getpid());
      printf(" \nCurrent value of num: %d", num);
      printf(" \nCurrent value of nump: %d", *nump);
      printf(" \nCurrent value of x: %d", x);

      x += 5;
      num ++;
      (*nump)++;

      printf("\nAFTER Increment, ");
      printf(" \nChild number: %d",i);
      printf(" \nChild process ID: %d",(int) getpid());
      printf(" \nCurrent value of num: %d", num);
      printf(" \nCurrent value of nump: %d", *nump);
      printf(" \nCurrent value of x: %d", x);

    }
    exit(0);
  }
  //parent process
  else
  {
    pid_t child;
    while((child = wait(NULL)) != -1) {
      printf("\nChild Process ended, Child PID: %d", (int)child);
    }
  }

  return 0;
}

int main()
{
   int nump = 100;
   return concurrent(50, 2, &nump);
}