memset不起作用（C）

Question

char path[25500]= {};//iniatize
int visited[2500]= {0};//iniatialize
void fun();//protype

int main(){
    fun();
}

void fun(){
    visited[2300]=1;
    path[0]='9';
    printf("\n%d %s",visited[2300],path);
    memset(path,0,25500);//reset
    memset(visited,0,2500);//reset
    printf("\n %d %s",visited[2300],path);//to see if resetted
}

Outputs are:

1 9
1

I want to reset just like in the start. But as you can see, memset doesnot reset. My compiler is codeblocks.

Answer 1

memset(visited,0,2500);//reset

访问的是整数数组，因此应为

memset(visited, 0, 2500 * sizeof(int))

Answer 2

memset takes the number of bytes to set, not the number of elements. Change this line:

memset(visited,0,2500);

To something like this and it should work:

memset(visited, 0, 2500 * sizeof(int));
//or like this: memset(visited, 0, sizeof(visited));

Answer 3

memset(visited, 0, 2500)

sets 2500 bytes to 0 from where visited points to.

However visited referrs to much more memory, namely 2500 times the size of its elements' type. That is 2550 * sizeof(visitied[0]) .

So do

    memset(visited, 0, 2500 * sizeof(visited[0])

to 0 out all of visited .

Your code uses the 2300th element. So assuming the size of an element to be 4 it is at offset 9200 to visited , your code only 0 -out 2500 bytes, so the 2300th element stays untouched by the call to memset() .

---

Referring to tthe comment below: Her a complete snippet on a robust way to use memset() in the OP's context:

#define VISITED_MAXIMUM (2500)

int visited[VISITED_MAXIMUM] = {0} /* line 3 */

/* Tons of code here . */

memset(visited, 0, VISITED_MAXIMUM * sizeof(*visited)); /* line X */

This construct above (line X) would survive without adjustements the change to dynamical memory allocation by replacing line 3 to be:

int * visited = calloc(VISITED_MAXIMUM, sizeof(*visited));
if (NULL == visited)
  exit(1);