Question

当我运行以下代码时出现错误;

编程接收信号SIGSEGV，分段故障。来自/lib64/libc.so.6的__GI__IO_vfscanf（）中的0x00007ffff7a74402 缺少单独的debuginfos，请使用：debuginfo-install 的glibc-2.17-78.el7.x86_64

我使用gcc warnings enable（-Wall）运行我的代码并逐步调试它。该错误在获取多维数组元素的行中。当我到达等级[1] [2]的步骤时，它表示无法访问地址0x00007ffff7a74402的内存。代码有什么问题？

 #include <stdio.h>

    //_________Prototypes________//

    int calcHighest(int grades[][4],int);
    int calcLowest(int grades[][4],int);
    int calcAverage(int grades[][4],int);

    int main (void){

      int funcSelection,nbOfStudent;
      int grades[nbOfStudent][4];
      int i,j;

      scanf("%d",&funcSelection);

     //check is one 1,2,3 and a number
      if(funcSelection <= 0 || funcSelection > 3){
        printf("Invalid Input.Please enter 1,2 or 3\n");
          return 1;
      }

      scanf("%d",&nbOfStudent);
     //check if it is positive and a number
      if(nbOfStudent <= 0){
        printf("Please enter a non-negative number\n");
         return 1;
      }

      for(i = 0;i < nbOfStudent;i++){
         for(j =0;j<4;j++){
           scanf("%d",&grades[i][j]);
         }
       }

      for(i = 0;i < nbOfStudent;i++){
         for(j =0;j<4;j++){
           scanf("%d",&grades[i][j]);
         }
       }

      if(funcSelection == 1){

        printf("%d\n",calcLowest(grades,nbOfStudent));
      }else if(funcSelection == 2){
        printf("%d\n",calcHighest(grades,nbOfStudent));
      }else{
        printf("%d\n",calcAverage(grades,nbOfStudent));
      }
      return 0;

    }

Answer 1

这就是问题所在：

int funcSelection,nbOfStudent;
int grades[nbOfStudent][4];

在nbOfStudent定义时，请考虑grades的值是什么。由于nbOfStudent未初始化，因此任何东西都可能是它的值，并且使用未初始化的变量会调用Undefinedial Behavior。

通过移动

解决问题

int grades[nbOfStudent][4];

后

scanf("%d",&nbOfStudent);
//check if it is positive and a number
if(nbOfStudent <= 0){
  printf("Please enter a non-negative number\n");
 return 1;
}

Answer 2

int funcSelection,nbOfStudent;
      int grades[nbOfStudent][4]; //problem leads to undefined behaviour
      int i,j;

nbofStudent不包含垃圾桶的任何值，导致未定义的行为。

解决方案：

在定义数组之前填充值nbofStudent。在你的情况下scanf为nbofStudent声明一个数组并检查变量的有效性。

scanf("%d",&nbOfStudent);
     //check if it is positive and a number
      if(nbOfStudent <= 0){
        printf("Please enter a non-negative number\n");
         return 1;
      }

应在这些说明之后定义变量。如此愚蠢地提到语句按顺序执行。

Answer 3

发布的代码包含多个错误和疏忽，包括：

无法提示用户提供学生人数
包含魔法＆＃39;数字如3和4
未能提示用户为每位学生提供成绩
无法提示用户使用哪种功能＆＃39;待执行
将int用于只能为正的值

这是我建议的代码

#include <stdio.h>
#include <stdlib.h>  // exit(), EXIT_FAILURE

#define NUM_GRADES (4)
#define MAX_FUNC   (3)

//_________Prototypes________//
int calcHighest(int grades[][ NUM_GRADES ], size_t);
int calcLowest( int grades[][ NUM_GRADES ], size_t);
int calcAverage(int grades[][ NUM_GRADES ], size_t);

int main (void)
{

    printf( "Enter number of Students: ");
    size_t nbOfStudent;
    if( 1 != scanf("%lu",&nbOfStudent) )
    { // then scanf for number of students failed
        perror( "scanf for number students failed");
        exit( EXIT_FAILURE );
    }

    // implied else, scanf successful

    //only declare array 'grades[][]' after knowing number of students
    int grades[nbOfStudent][ NUM_GRADES ];

    printf( "Enter %d grades for each of the %lu students: ", NUM_GRADES, nbOfStudent);
    for(size_t i = 0;i < nbOfStudent;i++)
    {
        for(size_t j=0; j<NUM_GRADES; j++)
        {
            scanf("%d",&grades[i][j]);
        }
    }


    printf( "1: calculate lowest student grade\n");
    printf( "2: calculate highest student grade\n");
    printf( "3: calculate average student grade\n");
    printf( "Enter Selection: ");
    size_t funcSelection;
    scanf("%lu",&funcSelection);
    if( 1 != scanf("%lu",&funcSelection) )
    { // then scanf for function selection failed
        perror( "scanf for function selection failed");
        exit( EXIT_FAILURE );
    }

    // implied else, scanf successful

    switch( funcSelection )
    {
        case 1:
            printf("%d\n",calcLowest(grades,nbOfStudent));
            break;

        case 2:
            printf("%d\n",calcHighest(grades,nbOfStudent));
            break;

        case 3:
            printf("%d\n",calcAverage(grades,nbOfStudent));
            break;

        case 0: // fall through
        default:
            printf("Invalid Input.Please enter 1,2 or 3\n");
            break;
    } // end switch

    return 0;
} // end function: main

采用多维数组元素时的分段错误

3 个答案: