Skip to content

Navigation Menu

Sign in
Appearance settings

Search code, repositories, users, issues, pull requests...

Provide feedback

We read every piece of feedback, and take your input very seriously.

Saved searches

Use saved searches to filter your results more quickly
Sign up
Appearance settings

Commit 3aafade

Browse files
authored
fix: remove potential segv from postfix_evaluation.cpp (TheAlgorithms#2995)
1 parent 43ce636 commit 3aafade

File tree

1 file changed

+36
-50
lines changed

1 file changed

+36
-50
lines changed

‎others/postfix_evaluation.cpp

Lines changed: 36 additions & 50 deletions
Original file line numberDiff line numberDiff line change
@@ -1,6 +1,7 @@
11
/**
22
* @file
3-
* @brief Evaluation of [Postfix Expression](https://en.wikipedia.org/wiki/Reverse_Polish_notation)
3+
* @brief Evaluation of [Postfix
4+
* Expression](https://en.wikipedia.org/wiki/Reverse_Polish_notation)
45
* @author [Darshana Sarma](https://github.com/Darshana-Sarma)
56
* @details
67
* Create a stack to store operands (or values).
@@ -11,9 +12,10 @@
1112
* When the expression is ended, the number in the stack is the final answer
1213
*/
1314
#include <algorithm> // for all_of
14-
#include <array> // for std::array
15+
#include <array> // for array
1516
#include <cassert> // for assert
1617
#include <iostream> // for io operations
18+
#include <stack> // for std::stack
1719
#include <string> // for stof
1820

1921
/**
@@ -26,36 +28,6 @@ namespace others {
2628
* @brief Functions for Postfix Expression algorithm
2729
*/
2830
namespace postfix_expression {
29-
/**
30-
* @brief Creates an array to be used as stack for storing values
31-
*/
32-
class Stack {
33-
public:
34-
std::array<float, 20> stack{}; ///< Array which will be used to store numbers in the input
35-
int stackTop = -1; ///< Represents the index of the last value added to array. -1 means array is empty
36-
};
37-
38-
/**
39-
* @brief Pushing operand, also called the number in the array to the stack
40-
* @param operand float value from the input array or evaluation
41-
* @param stack stack containing numbers
42-
* @returns none
43-
*/
44-
void push(float operand, Stack *stack) {
45-
stack->stackTop++;
46-
stack->stack[stack->stackTop] = operand;
47-
}
48-
49-
/**
50-
* @brief Popping operand, also called the number from the stack
51-
* @param stack stack containing numbers
52-
* @returns operand float on top of stack
53-
*/
54-
float pop(Stack *stack) {
55-
float operand = stack->stack[stack->stackTop];
56-
stack->stackTop--;
57-
return operand;
58-
}
5931

6032
/**
6133
* @brief Checks if scanned string is a number
@@ -74,28 +46,29 @@ bool is_number(const std::string &s) {
7446
* @param stack containing numbers
7547
* @returns none
7648
*/
77-
void evaluate(float a, float b, const std::string &operation, Stack *stack) {
49+
void evaluate(float a, float b, const std::string &operation,
50+
std::stack<float> &stack) {
7851
float c = 0;
7952
const char *op = operation.c_str();
8053
switch (*op) {
8154
case '+':
82-
c = a + b; // Addition of numbers
83-
others::postfix_expression::push(c, stack);
55+
c = a + b; // Addition of numbers
56+
stack.push(c);
8457
break;
8558

8659
case '-':
87-
c = a - b; // Subtraction of numbers
88-
others::postfix_expression::push(c, stack);
60+
c = a - b; // Subtraction of numbers
61+
stack.push(c);
8962
break;
9063

9164
case '*':
92-
c = a * b; // Multiplication of numbers
93-
others::postfix_expression::push(c, stack);
65+
c = a * b; // Multiplication of numbers
66+
stack.push(c);
9467
break;
9568

9669
case '/':
97-
c = a / b; // Division of numbers
98-
others::postfix_expression::push(c, stack);
70+
c = a / b; // Division of numbers
71+
stack.push(c);
9972
break;
10073

10174
default:
@@ -113,31 +86,32 @@ void evaluate(float a, float b, const std::string &operation, Stack *stack) {
11386
*/
11487
template <std::size_t N>
11588
float postfix_evaluation(std::array<std::string, N> input) {
116-
Stack stack;
89+
std::stack<float> stack;
11790
int j = 0;
11891

11992
while (j < N) {
12093
std::string scan = input[j];
12194
if (is_number(scan)) {
122-
push(std::stof(scan), &stack);
95+
stack.push(std::stof(scan));
12396

12497
} else {
125-
float op2 = pop(&stack);
126-
float op1 = pop(&stack);
98+
const float op2 = stack.top();
99+
stack.pop();
100+
const float op1 = stack.top();
101+
stack.pop();
127102

128-
evaluate(op1, op2, scan, &stack);
103+
evaluate(op1, op2, scan, stack);
129104
}
130105
j++;
131106
}
132107

133-
std::cout << stack.stack[stack.stackTop] << "\n";
108+
std::cout << stack.top() << "\n";
134109

135-
return stack.stack[stack.stackTop];
110+
return stack.top();
136111
}
137112
} // namespace postfix_expression
138113
} // namespace others
139114

140-
141115
/**
142116
* @brief Test function 1 with input array
143117
* {'2', '3', '1', '*', '+', '9', '-'}
@@ -153,7 +127,7 @@ static void test_function_1() {
153127

154128
/**
155129
* @brief Test function 2 with input array
156-
* {'1', '2', '+', '2', '/', '5', '*', '7', '+'}
130+
* {'100', '200', '+', '2', '/', '5', '*', '7', '+'}
157131
* @returns none
158132
*/
159133
static void test_function_2() {
@@ -164,13 +138,25 @@ static void test_function_2() {
164138
assert(answer == 757);
165139
}
166140

141+
static void test_function_3() {
142+
std::array<std::string, 43> input = {
143+
"1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "1",
144+
"1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "1",
145+
"+", "+", "+", "+", "+", "+", "+", "+", "+", "+", "+",
146+
"+", "+", "+", "+", "+", "+", "+", "+", "+", "+"};
147+
float answer = others::postfix_expression::postfix_evaluation(input);
148+
149+
assert(answer == 22);
150+
}
151+
167152
/**
168153
* @brief Main function
169154
* @returns 0 on exit
170155
*/
171156
int main() {
172157
test_function_1();
173158
test_function_2();
159+
test_function_3();
174160

175161
std::cout << "\nTest implementations passed!\n";
176162

0 commit comments

Comments
(0)

AltStyle によって変換されたページ (->オリジナル) /