c - C 中的 2D 数组指针访问段错误

Question

我正在尝试用 C 语言编写康威生命游戏的代码。我对包含我的宇宙的 2D 数组有一些问题。我将向您展示导致我出现问题的部分代码。实际上有两个问题我无法处理。

#include <stdio.h>
#include <stdlib.h>
#include "file2ppm.h"

typedef enum { false, true } bool;

void *allocateMemoryFor2DArray(int x, int y);                                   //allocate memory for 2D array
void initializeUniverseFromFile(char* path, int x, int y, int array[x][y]);     //set values of cells from a file   
void initializeUniverseRandomly(int x, int y, int array[x][y]);                 //set random values 
int getNumberOfColumns (FILE *file);                                            //get number of columns in file (yDim of Universe)
int getNumberOfLines (FILE *file);                                              //get number of lines in file (xDim of Universe)
void print2DArray (int x, int y, int array[x][y]);                              //print 2D array    
void setDimensionsFromFile(char* path,int* xDim, int* yDim, int* xDimB, int* yDimB);//set dimensions of Universe

int main(int argc, char * argv[])
{
    int i, j, n;        //loop indexes
    int nsteps;         //Number of generations
    int im, ip, jm, jp; //neighbour boundaries
    int yDim, xDim;     //Universe boundarier defined by user (Living area);
    int xDimB, yDimB;   //Universe boundaries expanded to each side by 1
    int nsum, isum;     //sum of neighbours, sum of alive cells after iteration
    //int **old, **new; //Universe 
    int (*old)[xDimB];      //Universe
    int (*new)[xDimB];      //Universe

    float x;            //to randomize first population
    char *inputPath;    //Path to file with ixDimBtial uxDimBverse
    char *outputPath;   //Path to output ppm files


    //temporary copy
    int yDim_copy, xDim_copy;

    printf("argc: %d\n", argc);
    switch (argc){
        case 4:         //Read the initial Universe from file
            //Take arguments
            nsteps = atoi(argv[1]); //Get number of iterations
            outputPath = argv[2];   //Get path for outputimages
            inputPath = argv[3];    //File with initialize uxDimBverse;
            setDimensionsFromFile(inputPath, &xDim, &yDim, &xDimB, &yDimB);
            old = allocateMemoryFor2DArray(xDimB, yDimB);   //Alocate memory for expanded Universes
            new = allocateMemoryFor2DArray(xDimB, yDimB);
            printf("Before initialize: yDim: %d, xDim: %d\n", yDim, xDim);      //Here the values are good
            //tmp copy
            yDim_copy = yDim;
            xDim_copy = xDim;
            initializeUniverseFromFile(inputPath, xDim, yDim, old);
            printf("After initialize: yDim: %d, xDim: %d\n", yDim, xDim);       //And here one dim is changed
            yDim = yDim_copy;       //I took a copy to avoid this problem for now
            xDim = xDim_copy;

            printf("After taking from copy: yDim: %d, xDim: %d\n", yDim, xDim);//Here dimensions are good again
            memcpy (new, old, xDimB*yDimB*sizeof(old[xDimB][yDimB]));           //Copy old to new
            break;


        default:
            printf("Usage: %s iter_number, output_name, yDim, xDim\n", argv[0]);
            printf("or\n");
            printf("Usage: %s iter_number, output_name, ixDimBtial_input_name\n", argv[0]);
            printf("Note: Initial file have to be in ./data/\n");
            return 1;
    }

    print2DArray(xDim, yDim, old);      //this works fine
    printf("In main: yDim: %d, xDim: %d\n", yDim, xDim);
    printf("%d\n", old[0][0]);          //this works fine
    printf("%d\n", old[2][2]);          //Segmentation failure

    return 0;
}

void *allocateMemoryFor2DArray(int x, int y){
    int (*array)[y] = malloc( sizeof(int[x][y]) );      //Allocate memory
    if (array == NULL) {                                /* always check the return of malloc */
        perror("malloc");
        exit(EXIT_FAILURE);
    }
    return array;
}

int getNumberOfColumns (FILE *file){
    int yDim = 0;
    char ch;

    do 
    {
        ch = getc(file);                            //Get 1 char from file

        if (ch == '\n')             //If ch is new line
        {
            rewind(file);           //Move file pointer to beginxDimBng of file
            return yDim;            //Found number of columns       
        }       
        else                
            ++yDim;

    }while (ch != EOF);
}

int getNumberOfLines (FILE *file){
    int xDim = 0;
    char ch;

    do  
    {
        ch = getc(file);                            //Get 1 char from file
        if(ch == '\n')                              //If new line
        {
            ++xDim;                             //Increase xDim (another row)
        }
    }while(ch != EOF);
    rewind(file);                                   //Move file pointer to beginxDimBng of file
    return xDim;
}


void print2DArray (int x, int y, int array[x][y])
{
    int i, j;
    printf("x: %d, y: %d\n", x, y);
    for (i = 1; i <= x; ++i) 
    {
        for (j = 1; j <= y; ++j) 
        {
            printf("%d ", array[i][j]);
        }
        printf("\n");
    }
}

void setDimensionsFromFile(char* path, int* xDim, int* yDim, int* xDimB, int* yDimB)
{
    FILE *file;
    int i,j;
    file = fopen(path, "r");        //open file 
    if (file)
    {
        *yDim = getNumberOfColumns (file);                  
        *xDim = getNumberOfLines (file);
        *xDimB = *xDim + 2;  // add 2 for left and right torus topology
        *yDimB = *yDim + 2;
        if (*xDim > 0 && *yDim > 0)
        {   
            printf("UxDimBverse dimension %d x %d\n", *xDim , *yDim);
        }           
        else
        { 
            perror("Wrong initialize file");
            exit(EXIT_FAILURE); 
        }       

        fclose(file);                       //Close file
    }
    else
    {
        perror("Open initialize file error");   
        exit(EXIT_FAILURE);
    }
}


void initializeUniverseFromFile(char* path, int x, int y, int array[x][y])
{ 
    FILE *file;
    int i,j;
    file = fopen(path, "r");        //open file 
    if (file)
    {
        //IxDimBtialize array
        char *ch;
        for (i = 1; i <= x; i++)
        {
            //printf("i: %d ", i);
            for (j = 1; j <= y; j++)
            {
                //printf("j: %d ", j);
                if (fscanf(file, "%c", ch) != 1)
                {
                    perror("Read error\n");
                }
                else if (isdigit((unsigned char)*ch))
                {
                    printf("%d", atoi(ch));
                    array[i][j] = atoi(ch);
                } 
                else 
                {
                    //printf("Numer znaku: %d ", ch);
                    j--;
                }
            }
            printf("\n");
        }
        printf("Done reading\n");
        fclose(file);           //Close file 
    } 
    else 
    {               //File open error
        perror("Open initialize file error");   
        exit (EXIT_FAILURE);
    }
    printf("In initialize yDim: %d, xDim: %d\n", x, y);
}

void initializeUniverseRandomly(int x, int y, int array[x][y])
{
    int i, j;
    float r;
    for (i = 1; i <= x; i++) {
        for (j = 1; j <= y; j++) {
            r = rand() / ((float)RAND_MAX + 1);
            if (r<0.5) {
                array[i][j] = i*x+j;
            }
            else {
                array[i][j] = i*x+j;
            }
        }
    }
}

问题1:我设置了宇宙的维度(变量 xDim 和 yDim)。我在第 45 行打印它们(检查注释//Here the value are good)。然后我调用 initializeUniverseFromFile(inputPath, xDim, yDim, old);并且其中一个尺寸值发生变化。我不知道为什么。这就是为什么我临时复制这个变量，因为我花了 2 个小时寻找那个错误。我什至在 initializeUniverseFromFile 函数的末尾打印出这些变量，它们都很好。但是当我再次回到 main 时(第 50 行)，该值发生了变化。这是小问题。更糟糕的是:

问题2我有一个指针 int (*old)[xDimB];

xDimB 是 xDim+2，因此它始终大于 xDim

我用函数初始化数组为2DArray分配内存(xDimB, yDimB)

然后我这样做:

print2DArray(xDim, yDim, old);      //this works fine
printf("In main: yDim: %d, xDim: %d\n", yDim, xDim); //Dimensions are fine
printf("%d\n", old[0][0]);          //this works fine
for (i=0; i<=xDim; ++i)
     printf("%d ", old[0][i];       //this works fine too
printf("%d\n", old[2][2]);          //Segmentation failure

用函数打印整个数组就可以了第一行的打印值很好从数组中间打印值创建错误。

Answer 1

I set the dimensions of universe (variables xDim and yDim)

在声明 VLA int (*old)[xDimB]; 和 int (*new)[xDimB] 之前，您需要这些包含有效数字。 ;。当 xDim 和 yDim 具有已知的、经过验证的值时，将这些 VLA 声明移至程序的后面一点。