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std::cout, std::wcout

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< cpp‎ | io
Revision as of 12:52, 21 January 2013 by Radix (Talk | contribs)

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Defined in header <iostream>
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extern std::ostream cout;
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extern std::wostream wcout;
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The global objects std::cout and std::wcout control output to a stream buffer of implementation-defined type (derived from std::streambuf), associated with the standard C output stream stdout.

These objects are guaranteed to be constructed before the first constructor of a static object is called and they are guaranteed to outlive the last destructor of a static object, so that it is always possible to write to std::cout in user code.

Unless sync_with_stdio(false) has been issued, it is safe to concurrently access these objects from multiple threads for both formatted and unformatted output.

Once initialized, std::cout is tie()'d to std::cin and std::wcout is tie()'d to std::wcin, meaning that any input operation on std::cin executes std::cout.flush() (via std::basic_istream::sentry's constructor).

Once initialized, std::cout is also tie()'d to std::cerr and std::wcout is tie()'d to std::wcerr, meaning that any output operation on std::cerr executes std::cout.flush() (via std::basic_ostream::sentry's constructor) (since C++11)

Example

#include <iostream>
struct Foo {
    int n;
    Foo() {
       std::cout << "static constructor\n";
    }
    ~Foo() {
       std::cout << "static destructor\n";
    }
};
Foo f; // static object
int main()
{
    std::cout << "main function\n";
}

Output:

static constructor
main function
static destructor

See also

Template:cpp/io/ios base/dcl list InitTemplate:cpp/io/dcl list clogTemplate:cpp/io/dcl list cout