Why is reading lines from stdin much slower in C++ than in Python?

Question

Aryan Kumar · Answer

There are a few reasons why reading lines from stdin is much slower in C++ than in Python.

Python's readline() function is more efficient. The readline() function in Python is a built-in function that is specifically designed to read lines from stdin. The readline() function in C++ is not a built-in function, and it is implemented using the std::cin object. The std::cin object is a general-purpose input stream that can be used to read data from a variety of sources, including stdin. However, the std::cin object is not as efficient as the readline() function in Python.
Python's readline() function is multithreaded. The readline() function in Python is multithreaded, which means that it can read lines from stdin in parallel. The std::cin object in C++ is not multithreaded, which means that it can only read lines from stdin sequentially.
Python's readline() function is optimized for stdin. The readline() function in Python is optimized for reading lines from stdin. The std::cin object in C++ is not optimized for reading lines from stdin.

As a result of these factors, the readline() function in Python is much faster than the std::cin object in C++.

Here is an example of how to read lines from stdin in Python and C++:

Python

def read_lines_from_stdin():
  lines = []
  while True:
    line = input()
    if line == "":
      break
    lines.append(line)
  return lines

lines = read_lines_from_stdin()

for line in lines:
  print(line)

C++

#include <iostream>

int main() {
  std::string line;
  while (std::getline(std::cin, line)) {
    std::cout << line << std::endl;
  }
  return 0;
}

The Python code will read lines from stdin and print them to the console. The C++ code will also read lines from stdin and print them to the console. However, the Python code will be much faster than the C++ code.

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Why is reading lines from stdin much slower in C++ than in Python?

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