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

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_x000D_ _x000D_ I wanted to compare reading lines of string input from stdin using Python and C++ and was shocked to see my C++ code run an order of magnitude slower than the equivalent Python code. Since my C++ is rusty and I'm not yet an expert Pythonista, please tell me if I'm doing something wrong or if I'm misunderstanding something. (TLDR answer: include the statement: cin.sync_with_stdio(false) or just use fgets instead. TLDR results: scroll all the way down to the bottom of my question and look at the table.) C++ code: #include #include using namespace std; int main() { string input_line; long line_count = 0; time_t start = time(NULL); int sec; int lps; while (cin) { getline(cin, input_line); if (!cin.eof()) line_count++; }; sec = (int) time(NULL) - start; cerr << "Read " << line_count << " lines in " << sec << " seconds."; if (sec > 0) { lps = line_count / sec; cerr << " LPS: " << lps << endl; } else cerr << endl; return 0; } // Compiled with: // g++ -O3 -o readline_test_cpp foo.cpp Python Equivalent: #!/usr/bin/env python import time import sys count = 0 start = time.time() for line in sys.stdin: count += 1 delta_sec = int(time.time() - start_time) if delta_sec >= 0: lines_per_sec = int(round(count/delta_sec)) print("Read {0} lines in {1} seconds. LPS: {2}".format(count, delta_sec, lines_per_sec)) Here are my results: $ cat test_lines | ./readline_test_cpp Read 5570000 lines in 9 seconds. LPS: 618889 $cat test_lines | ./readline_test.py Read 5570000 lines in 1 seconds. LPS: 5570000 I should note that I tried this both under Mac OS X v10.6.8 (Snow Leopard) and Linux 2.6.32 (Red Hat Linux 6.2). The former is a MacBook Pro, and the latter is a very beefy server, not that this is too pertinent. $ for i in {1..5}; do echo "Test run $i at `date`"; echo -n "CPP:"; cat test_lines | ./readline_test_cpp ; echo -n "Python:"; cat test_lines | ./readline_test.py ; done Test run 1 at Mon Feb 20 21:29:28 EST 2012 CPP: Read 5570001 lines in 9 seconds. LPS: 618889 Python:Read 5570000 lines in 1 seconds. LPS: 5570000 Test run 2 at Mon Feb 20 21:29:39 EST 2012 CPP: Read 5570001 lines in 9 seconds. LPS: 618889 Python:Read 5570000 lines in 1 seconds. LPS: 5570000 Test run 3 at Mon Feb 20 21:29:50 EST 2012 CPP: Read 5570001 lines in 9 seconds. LPS: 618889 Python:Read 5570000 lines in 1 seconds. LPS: 5570000 Test run 4 at Mon Feb 20 21:30:01 EST 2012 CPP: Read 5570001 lines in 9 seconds. LPS: 618889 Python:Read 5570000 lines in 1 seconds. LPS: 5570000 Test run 5 at Mon Feb 20 21:30:11 EST 2012 CPP: Read 5570001 lines in 10 seconds. LPS: 557000 Python:Read 5570000 lines in 1 seconds. LPS: 5570000 Tiny benchmark addendum and recap For completeness, I thought I'd update the read speed for the same file on the same box with the original (synced) C++ code. Again, this is for a 100M line file on a fast disk. Here's the comparison, with several solutions/approaches: Implementation Lines per second python (default) 3,571,428 cin (default/naive) 819,672 cin (no sync) 12,500,000 fgets 14,285,714 wc (not fair comparison) 54,644,808

Posted on 16 Aug 2022, this text provides information on Facebook Marketing API related to Digital Marketing. Please note that while accuracy is prioritized, the data presented might not be entirely correct or up-to-date. This information is offered for general knowledge and informational purposes only, and should not be considered as a substitute for professional advice.

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