c - 如何修复编译项目时出现的警告

Question

任务:需要开发一个多进程应用程序。原始进程是管理器，接受键盘输入并控制子进程。按“+”键，添加一个新进程，“-”-删除最后添加的进程，“q”-程序结束。每个子进程在永恒循环中逐个字符地显示其自己唯一的字符串。同时，字符串输出操作必须是原子的，即输出过程必须同步，这样屏幕上的行就不会混淆。信号/事件应该用作同步方法。 我该如何纠正这些错误？

    #include <stdio.h>
    #include <stdlib.h>
    #include <ncurses.h>
    #include <time.h>
    #include <unistd.h>
    #include <signal.h>
    #include <string.h>
    #include <sys/wait.h>
    #define MAX_COUNT 10
    /*
    char strings[10][30] = {{"\r\n1) First process"}, {"\r\n2) Second process"}, {"\r\n3) Third process"}, {"\r\n4) Fourth process"}, {"\r\n5) Fifth process"} , {"\r\n6) Sixth process"}, {"\r\n7) Seventh process"},{"\r\n8) Eighth process"}, {"\r\n9) Ninth process"}, {"\r\n10) Tenth process"}};
    */

    char strings[10][30] = {{"1) First process"}, {"2) Second process"}, {"3) Third process"}, {"4) Fourth process"}, {"5) Fifth process"} , {"6) Sixth process"}, {"7) Seventh process"},{"8) Eighth process"}, {"9) Ninth process"}, {"10) Tenth process"}};

    int printFlag = 0;
    int flagEnd = 1;

    struct sigaction printSignal, endSignal;

    void canPrint(int signo)
    {
      printFlag = 1;
    }

    void setEndFlag(int signo)
    {
      flagEnd = 1;
    }

    int main(void)
    {
      int currentNum = 0;
      int processNumber = 0;

      int flag = 0;

      initscr();
      clear();
      noecho();
      refresh();

      printSignal.sa_handler = canPrint;
      sigaction(SIGUSR1,&printSignal,NULL);

      endSignal.sa_handler = setEndFlag;
      sigaction(SIGUSR2,&endSignal,NULL);

      char c = 0;
      int i = 0;

      pid_t cpid[MAX_COUNT];


      while(c!='q')
      {
        c = getchar();

        switch(c)
        {
          case '+':   
        if(processNumber < MAX_COUNT)
        {
          cpid[processNumber] = fork();   
          processNumber++;

          switch(cpid[processNumber-1])
          {
            case 0:
              flagEnd = 0;
              while(!flagEnd)
              {
            usleep(10000); 
            if(printFlag)
            {
              for(i=0; i<strlen(strings[processNumber-1]); i++)
              {
                if(flagEnd)         
                  return 0;

                printf("%c",strings[processNumber-1][i]);
                refresh();
                usleep(70000);
              }
              refresh();
              printFlag = 0;
              kill(getppid(),SIGUSR2);
            }
              }
              return 0;
              break;

            case -1:
              printf("Error!\n");
              break;

            default:  
              break;        
          }
        }
        break;

          case '-':
        if(processNumber > 0)
        {
          kill(cpid[processNumber-1],SIGUSR2);  
          waitpid(cpid[processNumber-1],NULL,NULL);//??? 

          processNumber--;  

          if (currentNum >= processNumber)  
          {
            currentNum = 0; 
            flag = 1;                       
            flagEnd = 1;    
          }

        }       
            break;
        }

        if(flagEnd && processNumber>0)       
        {
          flagEnd = 0;
          if(currentNum >= processNumber - 1)   
        currentNum = 0;              
          else if(!flag) currentNum++;     

          flag = 0;

          kill(cpid[currentNum],SIGUSR1); 
        } 
        refresh();        
      }


      if(cpid[processNumber-1]!=0)
        for(;processNumber>=0;processNumber--)
        {
          kill(cpid[processNumber-1],SIGUSR2);
          waitpid(cpid[processNumber-1],NULL,NULL);//???
        }

      clear();  
      endwin();

      return 0;
 }

Answer 1

w.c:97:46: warning: passing argument 3 of ‘waitpid’ makes integer from pointer without a cast [-Wint-conversion]
           waitpid(cpid[processNumber-1],NULL,NULL);//???

In file included from w.c:8:0:
/usr/include/arm-linux-gnueabihf/sys/wait.h:86:16: note: expected ‘int’ but argument is of type ‘void *’
 extern __pid_t waitpid (__pid_t __pid, int *__stat_loc, int __options);

第三个参数必须是 int，NULL 不是 int 而是指针 (((void*) 0 ) 正如您在警告中看到的那样)，将其替换为 0，因此 waitpid(cpid[processNumber-1], NULL, 0);