I want to implement a stack but printf throws a segmentation fault - c

Question

I want to implement a stack using structures in C. Unfortunately, printf throws a segmentation fault. Perhaps there is a problem with dynamic allocation. Does anyone know how to solve it?
I have been facing this issue for the last two days. Your help will be very helpful for my study.
Here is my code
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#define SIZE 256
typedef int (*pf)();
typedef struct _stack{
int arr[SIZE];
int top;
pf push, pop, peek, isEmpty, size, clear, print;
} stack;
void *nstack(){
stack *pstack = (stack *)malloc(sizeof(stack));
void push(int data) {
if(pstack->top < SIZE-1) pstack->arr[++pstack->top]=data;
}
int pop() {
return (pstack->top >= 0)?pstack->arr[pstack->top--]:0;
}
int peek(){
return (pstack->top >= 0)?pstack->arr[pstack->top]:0;
}
bool isEmpty(){
return (pstack->top >= 0)?false:true;
}
int size(){
return pstack->top+1;
}
void clear(){
pstack->top = -1;
}
void print(){
if(!isEmpty()){
for(int i = 0; i <= pstack->top; i++) printf("%d", pstack->arr[i]);
printf("\n");
}
}
pstack->push=push;
pstack->pop=pop;
pstack->peek=peek;
pstack->isEmpty=isEmpty;
pstack->size=size;
pstack->clear=clear;
pstack->print=print;
pstack->top=-1;
return pstack;
}
void dstack(stack *pstack){
free(pstack);
}
void main() {
stack *A = nstack();
A->push(1);
A->push(4);
A->push(6);
printf("%d",A->pop());
printf("%d",A->pop());
dstack(A);
}

Answer 1

While the code compiles (with warning), it try to leverage GCC extensions for functions within functions. However, the internal functions must be called within a valid context - they try to access the local pstackof the nstack function - but it does not exists.
While this style work in many OO langauges (Java, and possibly C++), that support 'closures' or lambda, it does not work for C. Consider changing the interface for each of the function to take stack *, and change the calling sequence to pass it.
void push(stack *pstack, int data) {
if(pstack->top < SIZE-1) pstack->arr[++pstack->top]=data;
}
main() {
...
A->push(A, 1) ;
...
printf("%d", A->pop(A) ;
}

Answer 2

Really, you should edit your question and provide the exact errors but I've decided to do some of the legwork for you since you're probably pretty new to this.
So first thing I did was compile your code here with -Wall and look what I get:
SO_stack.c: In function ‘nstack’:
SO_stack.c:49:17: warning: assignment from incompatible pointer type [-Wincompatible-pointer-types]
pstack->push=push;
^
SO_stack.c:52:20: warning: assignment from incompatible pointer type [-Wincompatible-pointer-types]
pstack->isEmpty=isEmpty;
^
SO_stack.c:54:18: warning: assignment from incompatible pointer type [-Wincompatible-pointer-types]
pstack->clear=clear;
^
SO_stack.c:55:18: warning: assignment from incompatible pointer type [-Wincompatible-pointer-types]
pstack->print=print;
^
SO_stack.c: At top level:
SO_stack.c:66:6: warning: return type of ‘main’ is not ‘int’ [-Wmain]
void main() {
Let's look at the first error on line 49: pstack->push=push;
You've defined push function prototype as: void push(int data) but pstack->push is of type pf which is defined as int (*pf)(); See the problem here? You're trying to pass an argument to a function pointer that is not properly defined to handle the argument AND the return type is different. This is totally wrong. Your push(int data) implementation declares a return type of void and a parameter of int yet your pointer to this function declares a return type of int and a parameter of void. This is the case with push, isEmpty, clear, and print. You're going to have to decide if all of these functions need to have the same prototype or if you need to create several different function pointer types to handle them, etc...
So that's the first problem.
Second problem is that as the warning says, you have a void main() prototype for your main function. You should return int from main and specify a return code to the caller of main (likely the OS)... Commonly, successful execution returns 0 and failure returns -1 but this is specific to the platform so you can instead return EXIT_SUCCESS on success and return EXIT_FAILURE upon failure from main. For this macros to be defined, you need to have #include <stdlib.h> present, which you do.
Next issue is that as a commenter wrote, you should learn to use a debugger such as GDB, LLDB, or Windows Debugger so that you can figure out exactly where the program crashes.
I've not re-written your program because it has so many issues that I don't think it would be constructive to do so in this iteration, however, provide an exact error next time, and use the debugger to see if the crash happens inside of the actual printf() code as you implied, or it happens because you supplied corrupt memory to the printf function. My guess is that it is the latter... Meaning, it is in fact probably your code which is flawed and supplying an invalid char * to printf which is either out of bounds, nonexistent, etc... This is precisely what you will use a debugger to find out, by placing a breakpoint before the trouble code and watching the memory to see what's going on.
You need to either remove int data.
Work on this some more, and you will probably find the rest of the issues yourself, if there are any. You should compile with flag -Wall and consider compiling with flag -Werror to clear this kind of stuff up yourself in the future.