I'm writing a Calculator in C from scratch (homework assignment) and have troubles with memory somewhere.. The algorithm works perfectly, but I'm getting a set of Valgrind errors/warnings, e.g.:
echo -n "1" | valgrind ./a.out --track-origins=yes
==14261== Conditional jump or move depends on uninitialised value(s)
==14261== at 0x400B9F: create_rpn (main.c:53)
==14261== by 0x400742: main (main.c:253)
My makefile:
all:
gcc main.c -g -O2 -Wall -Werror -std=c99
My source code is below (and on GitHub). Can you help with it? Thank you in advance!
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_LEN 1024
// needs to check priority
int get_power(char op) {
if (op == '+') {
return 2;
} else if (op == '-') {
return 2;
} else if (op == '*') {
return 4;
} else if (op == '/') {
return 4;
} else {
return 0;
}
}
// checks if current char is operator
int is_operator(char op) {
if (op == '+' || op == '-' || op == '*' || op == '/') {
return 1;
} else {
return 0;
}
}
// checks if current char is digit
int is_digit(char op) {
if ((op >= '0' && op <= '9') || op == '.') {
return 1;
} else {
return 0;
}
}
// evaulates array in Postfix
double evaulate_rpn(char** exp, size_t len) {
double* stack = (double* ) malloc(len*sizeof(double)); // stack for operands
double a1 = 0.0;
double a2 = 0.0; // buffers to save stack items
size_t place = 0; // current stack size
for (size_t i = 0; i < len; ++i) {
if (is_operator(*exp[i]) == 1) {
// takes out last 2 operands, processes
if (place > 1) {
a1 = stack[place - 2];
a2 = stack[place - 1];
if (strncmp(exp[i], "+", 1) == 0) {
stack[place - 2] = a1 + a2;
} else if (strncmp(exp[i], "-", 1) == 0) {
stack[place - 2] = a1 - a2;
} else if (strncmp(exp[i], "*", 1) == 0) {
stack[place - 2] = a1 * a2;
} else if (strncmp(exp[i], "/", 1) == 0) {
stack[place - 2] = a1 / a2;
}
place -= 1;
} else if (place == 1) {
// unary minus, unary plus..
a1 = stack[place - 1];
if (strncmp(exp[i], "-", 1) == 0) {
stack[place - 1] = 0 - a1;
} else if (strncmp(exp[i], "+", 1) == 0) {
stack[place - 1] = a1;
}
} else {
// wrong order / anything else
printf("[error]");
exit(0);
}
} else {
// is operand -> convert char to double -> save double to stack
stack[place] = atof(exp[i]);
place++ ;
}
}
float res = stack[0];
free(stack);
return res; // result here
}
void push_to_stack(char*** reverse, size_t* inited_lines, size_t* used_lines, char* item, size_t size) {
if(*inited_lines <= *used_lines){
*inited_lines *= 2;
char** buf = (char** ) realloc(*reverse, (*inited_lines)*sizeof(char** ));
if (buf) {
*reverse = buf;
} else {
printf("[error]");
exit(0);
}
}
char* str = calloc(size + 1, sizeof(char));
if (str) {
memcpy(str, item, size + 1);
str[size] = '\0';
(*reverse)[*used_lines] = str;
(*used_lines)++ ;
} else {
printf("[error]");
exit(0);
}
}
// transform from Infix to Postfix notation
double create_rpn(char* exp, size_t len){
// stack of chars for operands ()+-*/
char* stack = (char* ) malloc(len);
if (stack == NULL) {
printf("[error]");
exit(0);
}
size_t stack_top = 0; // position of last item in stack
// array of numbers
size_t inited_lines = 1;
size_t used_lines = 0;
char** reverse = (char** ) malloc(inited_lines*sizeof(char* ));
if (reverse == NULL) {
printf("[error]");
exit(0);
}
char buffer = 0;
int bracket_deep = 0;
int digit = 0; // flag to start parsing Numbers/digits
size_t start_index = 0; // for parsing Long-Vals
size_t index = 0;
while (index <= len) {
buffer = exp[index]; // buffer constats only 1 char but it is a string
if (is_digit(buffer) == 1) {
// save first digit place
if (digit == 0) {
start_index = index;
digit = 1;
}
} else {
// push to stack when Num is over
if (digit == 1) {
digit = 0;
size_t size = index - start_index; // size of str
push_to_stack(&reverse, &inited_lines, &used_lines, exp + start_index, size);
}
// push Operands + check priority
if (is_operator(buffer) == 1) {
size_t power = get_power(buffer);
for (int i = stack_top - 1; i >= 0; --i) {
if (stack[i] == '(') {
break;
}
if (get_power(stack[i]) >= power) {
push_to_stack(&reverse, &inited_lines, &used_lines, &stack[i], 1);
stack_top-- ;
}
}
// push current Operand to stack
stack[stack_top++ ] = buffer;
} else if (buffer == '(') {
stack[stack_top++ ] = buffer;
bracket_deep++ ;
} else if (buffer == ')') {
// push operands to result
bracket_deep-- ;
stack_top-- ; // if no, '' will be added to output
while (stack[stack_top] != '(') {
push_to_stack(&reverse, &inited_lines, &used_lines, &stack[stack_top], 1);
if (stack_top > 0) {
stack_top-- ;
} else {
break;
}
}
} else if (buffer == ' ' || buffer == '\n') {
// ignore this case
} else if (buffer == '\0') {
for (int i = stack_top - 1; i >= 0; --i) {
push_to_stack(&reverse, &inited_lines, &used_lines, &stack[i], 1);
}
stack_top = 0;
} else {
printf("[error]"); // - wrong char: '%s', %c\n", buffer, *buffer); // wrong char!
exit(0);
}
}
if (bracket_deep < 0) {
printf("[error]"); // wrong bracket expr
exit(0);
}
index++ ;
}
free(stack);
if (bracket_deep == 0) {
double res = evaulate_rpn(reverse, used_lines);
for (int i = 0; i < inited_lines; i++) {
free(reverse[i]);
}
free(reverse);
return res;
} else {
printf("[error]"); // wrong brackets
exit(0);
}
}
int main() {
char* expression = (char* ) malloc(MAX_LEN*sizeof(char));
if (expression) {
size_t len = 0;
while (scanf("%c", &expression[len]) != -1) { // switch to getch ???
if (expression[len] != ' ') { // save everything except spaces
len++ ;
}
}
double result = create_rpn(expression, len);
printf("%.2f", result);
free(expression);
} else {
printf("[error]");
exit(0);
}
return 0;
}
You are reading 1 byte beyond the array bound, because your while loop in create_rpn() is
while (index <= len)
but should be
while (index < len)
/* ^ without the = */
since arrays are 0 indexed, exp[len] is beyond the array.
Also
Avoid redundant parentheses, they make the code ugly and hence, hard to read and understand.
Do not cast the return value of malloc(), read the link and you will understand why.
Another tip to make your code clearer, is to avoid mixing code with declarations, for a compiler it's easy to see a variable's scope, but not for the eyes.
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