5.29 time study punch (malloc pointer is passed trap)

First give an example

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

typedef struct { 

    int Data [the MaxSize];
     // save the element stack 
    int Top;
     // stack pointer 
} SqStack; 

// initialize stack 
void InitStack (SqStack * ST) { 
    ST = (SqStack *) the malloc ( the sizeof (SqStack)); 
    ST -> Top = 0 ; 
    the printf ( " initialization stack complete \ n- " ); 
} 

int main () { 
    SqStack * St; 
    InitStack (St); 
        printf ( "%d",st->top);
}

This is a stack of the initialization sequence, but the run will find the last printf statement did not execute, even if we will stack pointer as a parameter passed to St initialization function, the initialization function of its allocated space, but due to re-address malloc carried out the assignment, operation after operation so it is not the original parameters.