Question

我希望它根据文件中的值创建一个2D数组。我可以通过使用以下代码使数组成为本地来实现此目的：

int main()
{
    int a = 5; //this is from a file
    int b = 6; //this is from a file
    int (*array2d)[a] = malloc(sizeof(int)*a*b);

    return 0;
}

但是，我希望array2d是全球性的。以下不起作用：

int **array2d

int main()
{
    int a = 5; //this is from a file
    int b = 6; //this is from a file
    (*array2d)[a] = malloc(sizeof(int)*a*b);

    return 0;
}

有没有简单的方法可以做到这一点？

Answer 1

可以使用函数对2D数组的内存进行分配和取消分配：

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

int ** allocIntArray(int nrows, int ncols)
// allocate memory for 2D array and returns pointer if successful or NULL if failed
{
    int r, c; // rows and cols counters
    int ** parray; // pointer to array
    // allocate memory for rows pointers
    parray = (int **) malloc(nrows * sizeof(int *));
    if( parray == NULL) // check
    {
        return NULL; // error sign
    }
    // allocate memory for each row
    for (r = 0; r < nrows; r++)
    {
        parray[r] = (int*) malloc(ncols * sizeof(int));
        if( parray[r] == NULL ) // check
        {
            // clean memory that was allocated before error
            while(--r >= 0)
            {
                free(parray[r]);
            }
            free(parray);
            return NULL; // error sign
        }
    }
    // return when success 
    return parray;
}

int freeIntArray(int nrows, int **parray)
// frees memory allocated for 2D array and returns 1 if successful or 0 if failed
{
    int r; // rows counter
    if( parray == NULL || nrows < 1)
    {
        return 0;
    }
    // free memory allocated for each row
    for (r = 0; r < nrows; r++)
    {
        if(parray[r] != NULL)
        {
            free(parray[r]);
        }
    }
    // free memory allocated for rows pointers
    free(parray);
    return 1;
}

有了这两个函数，你可以创建任何大小的数组，例如：

int ** globArr;
int nrows; // number of rows
int ncols; // number of columns

int main(int argc, char * argv[])
{
    // let's filename is in argv[1]
    if( argc < 2) // we have not filename
    {
        printf("File name must be given as command line argument!\n");
        return 1;  // exit from program
    }
    // when we have filename try to use it
    FILE * f = fopen(argv[1], "r");

    if( f == NULL )  // we cannot read from file
    {
        printf("File %s cannot be read!\n", argv[1]);
        return 2;   // exit from program
    }
    // when we have file openned for reading
    //  we try to read first two numbers and use them as size of array
    if( 2 != fscanf(f, "%d %d", &nrows, &ncols) )   // we cannot read two numbers
    {
        printf("ERROR: Wrong file format!\n");
        return 3;   // exit
    }
    // check that numbers are positive
    if( nrows < 1 || ncols < 1 )
    {
        printf("ERROR: Wrong data size!\n");
        return 4;   // exit
    }
    //  now we can allocate memory
    globArr = allocIntArray(nrows, ncols);
    // check that array allocated
    if(globArr == NULL)
    {
        printf("ERROR: Cannot allocate memory!\n");
        return 5;   // exit
    }
    // and start a loop to read data from file
    int r, c;
    for(r = 0; r < nrows; r++)
    {
       for(c = 0; c < ncols; c++)
       {
          if (feof(f)) // end of file reached 
          {
              printf("ERROR: Unexpected end of file!\n");
              return 6; // exit
          }
          if( 1 != fscanf(f, "%d", &globArr[r][c]) )
          {
              printf("ERROR: Wrong file format!\n");
              return 6; // exit
          }
       }
    }
    fclose(f);
    // Now work with data
    // . . .

    return freeIntArray(nrows, globArr);
}

注意：文件格式可能与我的不同。我希望，该程序将以格式

读取文件

2 3
10 20 30
40 50 60

或

2 3 10 20 30 40 50 60

或

其中2和3定义了2d-array的大小

C - 基于文件初始化全局二维数组

1 个答案: