為什么這需要進行malloc？

Question

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

int main(){
    int * p = malloc(sizeof(int));
    *p = 10;
    *p += 10;
    printf("%d", *p);
}

如果它被分配了，它會給我正確的值，但是如果我將其聲明為：它將給我一個總線錯誤：

int main(){
        int * p;
        *p = 10;
        *p += 10;
        printf("%d", *p);
    }

Answer 1

未初始化的指針就是這樣。 初始化。 您期望它指向何處？ 它的值是不確定的，讀/寫它會導致不確定的行為。

它沒有提及動態分配的內存（ malloc ），但它必須是指有效的內存。 例如，這很好：

int main(void)
{
    int x;
    int *p = &x;
    *p = 10;
    *p += 10;
    printf("%d", *p);
}

Answer 2

#include<stdio.h>
#include<stdlib.h>
int main()
{

 int *ptr; 
 //*ptr=123;   Error here....Becuase it is like trying to store 
             //some thing into a variable without creating it first.

 ptr=malloc(sizeof(int)); // what malloc does is create a integer variable for you
                          // at runtime and returns its address to ptr,
                          // Which is same as if you assingned &some_variable 
                          // to ptr if it had been already present in your program.

 return 0;
}