Question

我正在尝试打印文件指针的位置（通过printpos（）函数），显示它在子节点和父节点中的位置。在编译我的代码时，我留下了这些错误：

xxxxxx@ubuntu:~/USP_ASG2$ gcc -o q1 q1.c 
/tmp/cc4zpABN.o: In function `main':
q1.c:(.text+0xdd): undefined reference to `printpos'
q1.c:(.text+0x171): undefined reference to `printpos'
q1.c:(.text+0x1fd): undefined reference to `printpos'
q1.c:(.text+0x2a4): undefined reference to `printpos'
collect2: error: ld returned 1 exit status

代码（供参考）：

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

int main()
{
  char x[3];
  x[0]='y';
  int ch;

  while(x[0]=='y'||x[0]=='Y')
  {
  int status;
  pid_t pid;

  int a = 123456;
  float b = 123.456;
  char c = 'Z';
  char buff[5];
  int fd = open("/proc/meminfo", O_RDONLY);

  //Retriving address's
  void *ap=&a, *bp=&b, *cp=&c;

    printf("\n---------------Initial Values---------------\n");
    printf("Parent Values:\n");
    printf("Integer a: \tvalue = %d, \taddress = %p\n", a, ap);
    printf("Float b: \tvalue = %f, \taddress = %p\n", b, bp);
    printf("Char c: \tvalue = %c, \t\taddress = %p\n", c, cp); 
    printpos("Pointer Position: ", fd);

    pid = fork();

  if(pid > 0)
  {
    pid = wait(&status);
    printf("\nParent Changed Values:\n");
    printf("Integer a: \tvalue = %d, \taddress = %p\n", a, ap);
    printf("Float b: \tvalue = %f, \taddress = %p\n", b, bp);
    printf("Char c: \tvalue = %c, \t\taddress = %p\n", c, cp);
    printpos("Pointer Position: ", fd);

    sleep(1);
  }
  else if(pid == 0)
  {

    printf("\nChild Initial Values:\n");
    printf("Integer a: \tvalue = %d, \taddress = %p\n", a, ap);
    printf("Float b: \tvalue = %f, \taddress = %p\n", b, bp);
    printf("Char c: \tvalue = %c, \t\taddress = %p\n", c, cp);
    printpos("Pointer Position: ", fd);

    a = 654321;
    b = 654.321;
    c = 'A';
    read(fd, buff, 5);

    printf("\n---------------Changed Values---------------\n");
    printf("\nChild Changed Values:\n");
    printf("Integer a: \tvalue = %d, \taddress = %p\n", a, ap);
    printf("Float b: \tvalue = %f, \taddress = %p\n", b, bp);
    printf("Char c: \tvalue = %c, \t\taddress = %p\n", c, cp);
    printpos("Pointer Position: ", fd);

    return 0;
  }
  else
    printf("fork() did not work"); 

  if(pid >0)
  {
      printf("Run Again?(y/n):");
      fgets(x, 2, stdin);
      while ( (ch = fgetc(stdin)) != EOF && ch != '\n');
  }
  }

 return 0; 
}

Answer 1

您可以使用lseek和printf。

printf("Pointer Position: %lld\n", lseek(fd, 0, SEEK_CUR));

Answer 2

这里的问题是没有名为printpos的函数。以下是一些应该按预期执行的代码。

void printpos( char* text, int fd )
{
    off_t position;
    position = lseek( fd, 0, SEEK_CUR );
    if( position >= 0 )
    {
        printf( "%s%lld\n", text, (long long)position );
    }
    else
    {
        printf( "Error getting position in file\n" );
    }
}

[编辑：更新了代码以添加(long long)的{{1}}演员，因为在某些平台上它可能是不同的类型]

未定义参考＆＃39; printpos＆＃39;

2 个答案: