使用 c 编程将文件中的行放入二维数组

Question

I have a file with several lines that look like this:

-180 -90 56 67
-179 -90 56 99
-178 -90 56 99
...
180 -90 45 45
-180 -89 45 45

The first two columns of each line are longitude and latitude values respectively. Now what I want to do is put these lines in a two dimensional array called filearrray[i][j] where i is longitude indices and j is latitude indices. Below is my attempt to do this:

int main(int argc, char *argv[])
{
    FILE    *fp=NULL;
    FILE    FILEOUT[150];
    char    inpFname[81],FILEOUT[150];
    char    buf[8000];
    char*   filearray = malloc(sizeof(float) * (159*360));
    int     i,j;
    int     date = atoi(argv[1]);   


    sprintf(inpFname,"global_20%d.test.out",date);
    if ((fp=fopen(inpFname,"rt"))==NULL)
    {
        printf("\nERROR: Cannot open/read input file [%s]\n\n",inpFname);
        exit(1);
    } 

    i=0;
    j=0;
    while(fgets(buf,sizeof buf, fp))
    {
        if( i >= 359 )
        {
            i=0;
            j=j+1;
        }
        sprintf(filearray[i][j],"%s",buf);
        i=i+1;
        

    }
}

However upon compiling the program I get the following error:

  translate_ww3file.c:34:23: error: subscripted value is neither array nor pointer nor     vector
       sprintf(filearray[i][j],"%s",buf);

How do I tweak this code so I can get the desired results?

Answer 1

The line

char*   filearray = malloc(sizeof(float) * (159*360));

is wrong, for several reasons:

In that line, you are allocating space for 159*360 elements of type float . However, you are assigning that space to a char * . This does not make sense. If every element in the 2D array should be a float , then you should write this instead:

float (*filearray)[159] = malloc( sizeof(float) * (360*159) );

In the line above, it is necessary to write float (*filearray)[159] instead of float *filearray[159] , because the latter declares an array of 159 elements in which every element is a float* , whereas the former declares one pointer to an array of 159 elements in which every element is a float .

Also, the number 159 seems wrong. If latitudes are numbers between -90 and +90 inclusive, then there are 181 possible numbers, so you should be using the number 181 instead of 159 . For the same reason, you should probably be using the number 361 instead of 360 for the longitude.

However, later in your program, you use the line:

sprintf(filearray[i][j],"%s",buf);

This implies that you don't want every element of the 2D array to be a float , because you can't sprintf to a float . Instead, it appears that you want every element to be a string.

If you want every element of the 2D array to be a string, then you must allocate sufficient space for every string. Simply allocating sizeof(float) bytes for every string will not be sufficient.

Since the two numbers that follow the longitude and latitude in every line seem to be integers, it may be appropriate to make every element of the 2D array store these two numbers as a pair of int , instead of using strings. You could define the following type:

struct pair
{
    int number1;
    int number2;
};

You could then define your 2D array like this:

struct pair (*filearray)[181] = malloc( sizeof(struct pair) * (361*181) );

It is also worth noting that it is good programming practice to call free for every malloc call when you no longer need the memory (in this case at the end of your program).