cout-performance

A rough benchmark of std::cout with different settings.

Benchmark

Print Shakespeare's sonnets 1000 times to /dev/null.

The benchmark compares four variants:

• default std::cout with std::endl
• std::cout with std::ios_base::sync_with_stdio(false)
• std::cout using '\n' instead of std::endl
• puts() from the C stdio library

Environment:

• Apple M3
• Clang 21
• arm64-apple-darwin25.5

Results

Time in microseconds.

Run	Default	no sync with stdio	no std::endl	puts()
1.	2447149	2431388	437274	206680
2.	2424436	2431463	432456	207813
3.	2410315	2475041	436400	203624
4.	2686783	2428963	438486	206264
5.	2419577	2436221	438761	207542
6.	2423601	2431060	434446	206263
7.	2431216	2433978	433248	207782
8.	2425815	2442381	437799	205182
9.	2429051	2424418	440202	207931
10.	2448260	2433070	437079	209172
Avg.	2454620	2436798	436636	206825
50p	2427433	2432266	437079	207111
90p	2472112	2445647	438761	208055

Conclusions

• Disabling stdio synchronization had no measurable effect in this benchmark.
• Using '\n' instead of std::endl improved performance by approximately 5–6×.
• puts() from <stdio.h> was more than 2× faster than std::cout using '\n' instead of std::endl.