malloc之后的Int Array初始化

Question

I got this little question about this int array initialization after I did memory allocation. I got below error:

"Line 7 Error : expected expression before '{' token"

This is my code:

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

int main()
{
    int i;
    int *x=malloc(3*sizeof(int)); //allocation
    *x={1,2,3}; //(Line 7) trying to initialize. Also tried with x[]={1,2,3}.
    for(i=0;i<3;i++)
    {
        printf("%d ",x[i]);
    }
    return 0;
}

Is there any other way to initialize my array after I do memory allocation?

Answer 1

First of all, we must understand that the memory for array is allocated at heap memory area. Therefore we can initialize by following methods.

• using memcpy function
• pointer arithmetic

Above two methods preserve the memory allocation through malloc function. But assignment through (int[]) {1,2,3} will cause memory wastage due to previous allocated heap memory.

int* x = (int*) malloc(3 * sizeof(int));
printf("memory location x : %p\n",x);

// 1. using memcpy function
memcpy(x, (int []) {1,2,3}, 3 * sizeof(int) );
printf("memory location x : %p\n",x);


// 2. pointer arithmetic
*(x + 0) = 1;
*(x + 1) = 2;
*(x + 2) = 3;
printf("memory location x : %p\n",x);

// 3. assignment, useless in case of previous memory allocation
x = (int []) { 1, 2, 3 };
printf("memory location x : %p\n",x);