如何使用指向结构的指针填充数组

Question

I have to fill an array with pointers to structs. The struct is:

typedef struct {
  char* name;
  double weiten[3];
} springer;

Now I want to fill an array springer *spr[] . I have an array of strings called namen and n is the number of elements that I want to have in the array in the end.

The function to fill the array:

void fuellen(springer *spr[], const char* namen[], int n){
spr=calloc(n,sizeof(springer));
for(int i=0;i<n;i++){
    (*spr[i]).name=calloc(30,sizeof(char));
     strcpy((*spr[i]).name, namen[i]);
    spr[i]->weiten[0]=zufallsWeite();
    spr[i]->weiten[1]=zufallsWeite();
    spr[i]->weiten[2]=zufallsWeite();
}
}

So the structs that the array points to should be filled with structs that have the names in my char-array as names. The array that is also part of the structs should be filled with 3 randomly generated numers between 6 and 9 (zufallsWeite() gives you those.

Now in the main function I want to use the function:

const int N = 5;
const char *names[] = {"Tom Mueller","Timo Meier","Ulf Sommer","Tobi 
Winter","Uwe Schmidt"};

springer *spr[N];
fuellen(spr, names, N);

The build works but then the program shuts down and I get an error message. Can someone please tell me what I am doing wrong? I have been looking for a while but I have not found anything.

Answer 1

You have (comments added by me):

void fuellen(springer *spr[], const char* namen[], int n){
    // At this point, spr is a pointer to the first element in
    // the array that was passed into the funtion.
    spr=calloc(n,sizeof(springer));
    // Now spr, a local pointer value, points to zeroed memory in the heap.
    // The following loop copies strings from namen[] to spr[].
    for(int i=0;i<n;i++){
        //(*spr[i]).name=calloc(30,sizeof(char));
        //strcpy((*spr[i]).name, namen[i]);
        strdup(namen[i];)
        spr[i]->weiten[0]=zufallsWeite();
        spr[i]->weiten[1]=zufallsWeite();
        spr[i]->weiten[2]=zufallsWeite();
    }
    // Unfortunately, all that work, including the heap
    // allocation is lost when this function returns.
}

Just don't overwrite spr with a call to calloc .

void fuellen(springer *spr[], const char* namen[], int n){
    // spr[] was allocated by the caller!
    // Allocate each element of the array and initialize the struct.
    for(int i=0;i<n;i++){
        spr[i] = malloc(sizeof(springer));
        spr[i]->name = strdup(namen[i]);
        spr[i]->weiten[0]=zufallsWeite();
        spr[i]->weiten[1]=zufallsWeite();
        spr[i]->weiten[2]=zufallsWeite();
    }
}