Strcpy changing struct int array

Question

I have a struct in C, and I create an array of this struct

typedef struct {
    int aNum;
    char name[20];
    char sym[10];
    char class[30];
    float weight;
    int shell[SHELLS];
} element_t;
element_t elements[MAX_ELEMENTS];

I am asking the user for an input ( 1 Hydrogen H other_nonmetals 1.008 1 0 0 0 0 0 0 ), and I separate it into an array based on the spaces. I get each user input by calling a function,

for(int i=0;i<N;i++) 
    scan_element(i);

function:

void scan_element(int i) {
    char *array[12];
    char str[100];
    int j=0;
    if (fgets(str, 100, stdin)) {
        array[j] = strtok(str," ");
        while(array[j]!=NULL)
        {
            array[++j] = strtok(NULL," ");
        }
    }
    elements[i].aNum = (int) strtol(array[0], NULL, 10);
    if(i>0)
        for(int k=5;k<SHELLS+5;k++)
            printf("%d ",elements[i-1].shell[k]);
    printf("\n");
    strcpy(elements[i].name, array[1]);
    strcpy(elements[i].sym, array[2]);
    strcpy(elements[i].class, array[3]);
    elements[i].weight = (strtod(array[4],NULL));
    for(int k=5;k<SHELLS+5;k++)
        elements[i].shell[k] = (int) strtol(array[k], NULL, 10);
}

If I just input 1 element, the shell int array is fine, but when I input another element, it messes up the previous element's shell array. It should look like 1 0 0 0 0 0 0 , and it does for the current element, but when I input another element, the shell array looks like 1 0 82 1684104524 0 0 0 . I figured it happens after I call strcpy , as before it prints out fine, but right after the first time I call strcpy , it adds random numbers to the array.

How can I fix it so that so I can enter multiple elements without it messing up the previous element's shell array? It only messes up the shell array, nothing else from the previous struct.

Answer 1

The structure element int shell[SHELLS];

has index range from 0 to (SHELLS-1).

So the shell[0] .. shell[SHELLS-1] are valid.

The following assignment is out of bound assignment:

for(int k=5;k<SHELLS+5;k++)
    elements[i].shell[k] = (int) strtol(array[k], NULL, 10);

shell[SHELLS], shell[SHELLS+1], shell[SHELLS+2], shell[SHELLS+3] and shell[SHELLS+4] will be out of bound which causes undefined behaviors. Those numbers you see happened to be numbers in those out of bound memory space.

I think you want to do something like:

  int iShellCnt = 0;

  for(int k=5;k<SHELLS+5;k++)
      elements[i].shell[iShellCnt++] = (int) strtol(array[k], NULL, 10);

Answer 2

BTW: what is SHELLS defined as?

The following is the root of the problem:

The code block beginning with:

for(int k=5;k<SHELLS+5;k++) 

will place the first entry in

elements[i].shell[5] 

and continue placing data until long past the end of the shell[] array, This result is undefined behavior and can/will lead to a seg fault event.