C中全局指针与局部指针的动态内存分配

Question

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• Correctly allocating multi-dimensional arrays 2 answers

I am trying to assign values for a double pointer and I could not do it because when my pointer is locally declared it is working fine and when I declare it globally then it is not working. Here are the codes for the above mentioned scenarios

// Declared Globally, Not Working

#include<stdio.h>
#include<stdlib.h>
int **x;
int main() {
   x=(int**)malloc(sizeof(int*));
   x[1][2]=10;
   printf("%d",x[1][2]);
}

// Declared Locally, Working fine

#include<stdio.h>
#include<stdlib.h>
int main() {
   int **x;
   x=(int**)malloc(sizeof(int*));
   x[1][2]=10;
   printf("%d",x[1][2]);
}

Answer 1

In both cases it is invalid code. You need to allocate memory for the pointer(s) then for the object(s). You only malloc space for the pointer but not for the object.

It is the UB