C stack implementation throws bad access error -
am building stack in c. stack fails exc_bad_access error on if check in isempty() function, , i'm not sure why.
typedefs & definitions:
#define nodesize sizeof(stacknode) struct stacknode { int data; struct stacknode *nextptr; }; typedef struct stacknode stacknode; typedef stacknode *stacknodeptr; stack operation functions
void push(stacknodeptr *topptr, int value) { // declare new node , set top stacknode *node; node = malloc(sizeof(nodesize)); node->data = value; node->nextptr = *topptr; // reassign pointer top *topptr = node; printstack(*topptr); } int pop(stacknodeptr *topptr) { stacknode *node = *topptr; if (isempty(node)) { return 0; } // grab current top node , reset 1 beneath top pointer. *topptr = node->nextptr; printstack(*topptr); return node->data; } int isempty(stacknodeptr topptr) { if (topptr == null || topptr->nextptr == null) { // bad_access return 1; } return 0; } void printstack(stacknodeptr topptr) { stacknode *iter = topptr; // if stack empty, print that. if (!isempty(iter->nextptr)) { // iterate on each element in stack , print data (;isempty(iter); iter = iter->nextptr) { printf("%d ", iter->data); } printf("null"); } else { printf("null"); } printf("\n"); } void evaluatepostfixexpression(char *expr) { // create stack , insert initial parenthesis stacknode *head; head = malloc(nodesize); (int = 0; expr[i] != '\0'; i++) { char token = expr[i]; // if current character digit if (token >= '0' && token <= '9') { push(&head, token - '0'); // if it's operator } else if (token == '+' || token == '-' || token == '*' || token == '/' || token == '^' || token == '%') { int x = pop(&head); int y = pop(&head); int result = calculate(y, x, token); push(&head, result); } } int output = pop(&head); printf("the value of expression is: %d\n", output); } int calculate(int op1, int op2, char operator) { switch (operator) { case '+': return op1 + op2; case '-': return op1 - op2; case '*': return op1 * op2; case '/': return op1 / op2; case '%': return op1 % op2; } if (operator == '^') { int result = 1; (int = 0; < op2; i++) { result *= op1; } return result; } return 0; } even hint in right direction appreciated.
request context:
int main() { char postfix[255] = "54*81+4/+"; evaluatepostfixexpression(postfix); return 0; } void evaluatepostfixexpression(char *expr) { // create stack , insert initial parenthesis stacknode *head; head = malloc(nodesize); (int = 0; expr[i] != '\0'; i++) { char token = expr[i]; // if current character digit if (token >= '0' && token <= '9') { push(&head, token - '0'); // if it's operator } else if (token == '+' || token == '-' || token == '*' || token == '/' || token == '^' || token == '%') { int x = pop(&head); int y = pop(&head); int result = calculate(y, x, token); push(&head, result); } } int output = pop(&head); printf("the value of expression is: %d\n", output); } int calculate(int op1, int op2, char operator) { switch (operator) { case '+': return op1 + op2; case '-': return op1 - op2; case '*': return op1 * op2; case '/': return op1 / op2; case '%': return op1 % op2; } if (operator == '^') { int result = 1; (int = 0; < op2; i++) { result *= op1; } return result; } return 0; }
it looks expression
if (topptr == null || topptr->nextptr == null) is giving error because topptr doesn't point valid node, nor it's null. topptr->nextptr give error, due fact topptr not valid pointer.
according code, head->nextptr not initialized null, seems cause of problem.
by way: why initialize head variable empty node? far can see, use head = null , work.
last, not least: should free node variable in pop() function, in order avoid memory leak.
hope helps.
Comments
Post a Comment