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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 an application in C++ and I have certain constraints such as time limit for execution. My application has loads printing commands on the console. So which one would be preferable printf or cout?
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With synchronization turned off, the above results indicate that cin is 8-10% faster than scanf(). This is probably because scanf() interprets the format arguments at runtime and makes use of variable number of arguments, whereas cin does this at compile time.
As for why it is so "time consuming", (in other words, slow,) that's because the primary purpose of std::cout (and ultimately the operating system's standard output stream) is versatility, not performance.
Printf is a function which needs parameters and format specifiers (%d for int). Cout is stream oriented output stream object where you do not need any format specifiers. printf returns an integer value (the number of characters actually printed) and cout does not return anything.
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...
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Do you really need to care which has a faster execution speed? They are both used simply for printing text to the console/stdout, which typically isn't a task that demands ultra-high effiency. For that matter, I wouldn't imagine there to be a large difference in speed anyway (though one might expect printf to be marginally quicker because it lacks the minor complications of object-orientedness). Yet given that we're dealing with I/O operations here, even a minor difference would probably be swamped by the I/O overhead. Certainly, if you compared the equivalent methods for writing to files, that would be the case.
printf is simply the standard way to output text to stdout in C.
'cout' piping is simply the standard way to output text to stdout in C++.
Saying all this, there is a thread on the comp.lang.cc group discussing the same issue. Consensus does however seem to be that you should choose one over the other for reasons other than performance.
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