NAME

std::stack::push - std::stack::push

Synopsis

void push( const value_type& value );
void push( value_type&& value ); (since C++11)

Pushes the given element value to the top of the stack.

1) Effectively calls c.push_back(value)
2) Effectively calls c.push_back(std::move(value))

Parameters

value - the value of the element to push

Return value

(none)

Complexity

Equal to the complexity of Container::push_back.

Example

This program implements the famous DSL BrainHack, when std::stack is especially
convenient to collect paired brackets.

// Run this code

#include <map>
#include <stack>
#include <array>
#include <iostream>
#include <stdexcept>
#include <string_view>

class BrainHackInterpreter {
std::map<unsigned, unsigned> open_brackets, close_brackets;
unsigned program_pos_{0};
std::array<std::uint8_t, 32768> data_;
int data_pos_{0};

void collect_brackets_positions(const std::string_view program) {
std::stack<unsigned> brackets_stack;

for (auto pos{0U}; pos != program.length(); ++pos) {
const char c{program[pos]};
if ('[' == c) {
brackets_stack.push(pos);
} else if (']' == c) {
if (brackets_stack.empty()) {
throw std::runtime_error("brackets [] do not match!");
} else {
open_brackets[brackets_stack.top()] = pos;
close_brackets[pos] = brackets_stack.top();
brackets_stack.pop();
}
}
}

if (!brackets_stack.empty())
throw std::runtime_error("brackets [] do not match!");
}

void check_data_pos(int pos) {
if (pos < 0 or pos >= static_cast<int>(data_.size()))
throw std::out_of_range{"data pointer out of bound"};
}

public:
BrainHackInterpreter(const std::string_view program) {
collect_brackets_positions(program);
data_.fill(0);

for (; program_pos_ < program.length(); ++program_pos_) {
switch (program[program_pos_]) {
case '<': check_data_pos(--data_pos_); break;
case '>': check_data_pos(++data_pos_); break;
case '-': --data_[data_pos_]; break;
case '+': ++data_[data_pos_]; break;
case '.': std::cout << data_[data_pos_]; break;
case ',': std::cin >> data_[data_pos_]; break;
case '[':
if (data_[data_pos_] == 0)
program_pos_ = open_brackets[program_pos_];
break;
case ']':
if (data_[data_pos_] != 0)
program_pos_ = close_brackets[program_pos_];
break;
}
}
}
};

int main()
{
BrainHackInterpreter
{
"++++++++[>++>>++>++++>++++<<<<<-]>[<+++>>+++<-]>[<+"
"+>>>+<<-]<[>+>+<<-]>>>--------.<<+++++++++.<<----.>"
">>>>.<<<------.>..++.<++.+.-.>.<.>----.<--.++.>>>+."
};
}

Output:

Hi, cppreference!