cout and printf [duplicate]

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printf vs 开发者_如何学运维cout in C++

What are the differences between cout and printf?

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cout automatically make casts and finds out the type of the variables you are trying to print. So you can do something like:

int myint = 5;
cout << myint;

And cout will detect that myint is an int and print it. With printf, you have to specify what is the type of the variable you are trying to print:

int myint = 5;
printf("%d", myint);

Also, cout is slower than printf (because it does the type detection...), although in most practical applications, you won't notice the performance difference.

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printf is the function used for printing data on the standard output of the stdio library, the IO library of C. It's kept in C++ mainly for legacy reasons, although sometimes it's still useful.

cout is a C++ stream from the iostreams library (in particular, it's defined to be a ostream &); the iostreams library is the native C++ way to perform IO.

In general it's easier and safer to use iostreams than the old printf-like functions (thanks to << operator overloading instead of format strings+varargs), and it's the C++ "idiomatic" way to perform IO, so you should use it unless you have specific needs not to do so.

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Basically, cout is the C++ way of outputting to standard output while printf is the C way.

C++ iostreams (of which cout is one) are based on C++ classes and are extensible to handle new classes. In other words, you can create a class called foo and then do:

foo bar;
std::cout << bar << std::endl;

On the other hand, printf cannot handle new types, you have to write functions which call printf for each of the components of that type, where each component is already a type known to printf (such as int or char *).

There's really no excuse for using printf in C++ code. I always say that, if you're going to use C++, you should use it, not wallow in the old world :-) If you want to use printf, stick with C.

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If you're looking for an example of how to allow your class to be used in iostreams, see an answer I provided to an earlier question regarding the code that does it.

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taken from http://forums.devshed.com/c-programming-42/difference-between-cout-and-printf-38373.html

cout is an object of the iostream in C++. If you are using C++, then use cout, it works well. printf while doing some the same things, it is a formatting function that prints to the standard out. This is mainly used in C.

so printf is the big brother of cout in a way, as it allows you to format strings.