cout or printf which of the two has a faster execution speed C++?

Question

I have been coding in C++ for a long time. I always wondered which has a faster execution speed printf or cout?

Situation: I am designing a

Answer 1

On Windows at least, writing to the console is a huge bottleneck, so a "noisy" console mode program will be far slower than a silent one. So on that platform, slight differences in the library functions used to address the console will probably make no significant difference in practice.

On other platforms it may be different. Also it depends just how much console output you are doing, relative to other useful work.

Finally, it depends on your platform's implementation of the C and C++ I/O libraries.

So there is no general answer to this question.

Answer 2

Each has its own overheads. Depending on what you print, either may be faster.

Here are two points that come to mind -

printf() has to parse the "format" string and act upon it, which adds a cost.
cout has a more complex inheritance hierarchy and passes around objects.

In practice, the difference shouldn't matter for all but the weirdest cases. If you think it really matters - measure!

EDIT -
Oh, heck, I don't believe I'm doing this, but for the record, on my very specific test case, with my very specific machine and its very specific load, compiling in Release using MSVC -

Printing 150,000 "Hello, World!"s (without using endl) takes about -
90ms for printf(), 79ms for cout.

Printing 150,000 random doubles takes about -
3450ms for printf(), 3420ms for cout.

(averaged over 10 runs).

The differences are so slim this probably means nothing...

Answer 3

You should never need to ask this question, as the user will only be able to read slower than both of them.

If you need fast execution, don't use either.

As others have mentioned, use some kind of logging if you need a record of the operations.

Answer 4

I recently was working on a C++ console application on windows that copied files using CopyFileEx and was echoing the 'to' and 'from' paths to the console for each copy and then displaying the average throughput at the end of the operation.

When I ran the console application using printf to echo out the strings I was getting 4mb/sec, when replacing the printf with std::cout the throughput dropped to 800kb/sec.

I was wondering why the std::cout call was so much more expensive and even went so far as to echo out the same string on each copy to get a better comparison on the calls. I did multiple runs to even out the comparison, but the 4x difference persisted.

Then I found this answer on stackoverflow..

Switching on buffering for stdout did the trick, now my throughput numbers for printf and std::cout are pretty much the same.

I have not dug any deeper into how printf and cout differ in console output buffering, but setting the output buffer before I begin writing to the console solved my problem.

Answer 5

Anecdotical evidence:
I've once designed a logging class to use ostream operators - the implementation was insanely slow (for huge amounts of data).

I didn't analyze that to much, so it might as well have been caused by not using ostreams correctly, or simply due to the amount of data logged to disk. (The class has been scrapped because of the performance problems and in practice printf / fmtmsg style was preferred.)

I agree with the other replies that in most cases, it doesn't matter. If output really is a problem, you should consider ways to avoid / delay it, as the actual display updates typically cost more than a correctly implemented string build. Thousands of lines scrolling by within milliseconds isn't very informative anyway.

Answer 6

If you ever need to find out for performance reasons, something else is fundamentally wrong with your application - consider using some other logging facility or UI ;)