子功能中的C分段故障：如何知道要解决的问题？ 什么是细分错误？

Question

I keep getting a segmentation fault, but I'm not sure what that means or how to tell what is causing it (I'm very new to programming and C). In this function, called by main.c, I need to determine the index of the smallest number in eacg row of a two-dimentional array.

Here is my code:

#include "my.h"

void findfirstsmall (int x, int y, int** a)
{
    int i;
    int j;
    int small;  

    small = y - 1;


printf("x = %3d, y = %3d\n", x, y);                      //trying to debug


    printf("f.  The first index of the smallest number is: \n");
    for(i = 0; i < x; i++)
        {
           for(j = 0; j < y; i++)          <---------- needs to be j, for any future readers
               {
                  if(a[i][small] > a[i][j])
                        small = j;
printf("small = %3d\n", small);                          //trying to debug
               }
           printf("Row: %4d, Index: %4d\n", i, small);
           small = y - 1;
           printf("\n");
        }
    printf("\n");
    return;
}

It prints correctly for the first row, but not the second. This is my array:

56 7 25 89 4
-23 -56 2 99 -12

This is what I am getting when I run the program:

 x = 2, y = 5 f. The first index of the smallest number is: small = 4 small = 0 Segmentation fault 

This is in C. Thanks in advance for the help!

Answer 1

Fix the typo :

       for(j = 0; j < y; j++)
                         ^^

Answer 2

A segmentation error means that you are accessing memory that you do not own.

As a instant guess without looking at your code - it is an off-by-one-error. Remember C arrays are zero based.

I will look at your code more soon.

Answer 3

printf("f.  The first index of the smallest number is: \n");
for(i = 0; i < x; i++)
    {
       for(j = 0; j < y; i++) // my guess is that you increment "i" instead of "j"
           {

Answer 4

Note that there is a difference between a two-dimensional array and an array of pointers (see this question ). Depending on what you're doing in main() , this could be your problem. For example, the following would not work with the function as is, since it passes a pointer to memory containing an array of arrays:

int arr[2][5] = { {  56,   7,  25,  89,   4 },
                  { -23, -56,   2,  99, -12 } };
findfirstsmall (2, 5, arr);

However, this would be ok, since it passes an array of pointers to the start of each sub-array of arr :

int arr[2][5] = { {  56,   7,  25,  89,   4 },
                  { -23, -56,   2,  99, -12 } };
int *tmp[2];
tmp[0] = &arr[0][0];
tmp[1] = &arr[1][0];
findfirstsmall (2, 5, tmp);