.gitignore

/dummy
/infile.txt
/outfile.txt

README.md

The gist tries to reproduce the issue from the SO question about the difference in the output between executing the same command in a shell and in python.

1. Install git, make, g++, env, bash, python, diff

   For example, on Windows, you could install "git for Windows", "GnuWin32 make", "MinGW g++" and configure %PATH% correspondingly

2. Clone gist

    $ git clone https://gist.github.com/zed/dd44ade13d313ceb8ba8e384ba1ff1ac so-q
    $ cd so-q
   

3. Generate input data, build dummy c++, run the test:

    $ make
   

If you see: "Files infile.txt and outfile.txt are identical" then there is no difference (the test has failed to reproduce the issue).

dummy.cc

/** $ g++ dummy.cc -o dummy */
#include <iostream>


int main()
{
    int size, count, a, b;
    std::cin >> size;
    std::cin >> count;

    std::cout << size << " " << count << std::endl;


    for (int i = 0; i < count; ++i)
    {
        std::cin >> a >> b;
        std::cout << a << " " << b << std::endl;
    }
}

generate-infile.py

n = 100000
print(1, n)
for i in range(100000):
    print(i, i+i)

Makefile

test: user2346536.py dummy infile.txt
	env PATH=.:"$$PATH" python $<
	diff -s infile.txt outfile.txt

dummy: dummy.cc
	g++ $< -o $@

infile.txt: generate-infile.py
	python $< > $@

user2346536.py

# from http://stackoverflow.com/questions/37734470/why-is-subprocess-run-output-different-from-shell-output-of-same-command
import subprocess


with open('infile.txt', 'rb') as test_file:
    stdin = test_file.read()
    p = subprocess.run(['dummy'], input=stdin, stdout=subprocess.PIPE)
    out = p.stdout
    if stdin == out:
        print('OK')
with open('outfile.txt', "wb") as text_file:
    text_file.write(out)