Difference between revisions of "cpp/io/clog"
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| − | The global objects {{ | + | The global objects {{tt|std::clog}} and {{tt|std::wclog}} control output to a stream buffer of implementation-defined type (derived from {{lc|std::streambuf}}), associated with the standard C output stream {{lc|stderr}}, but, unlike {{lc|std::cerr}}/{{lc|std::wcerr}}, these streams are not automatically flushed and not automatically tie()'d with cout. |
These objects are guaranteed to be initialized during or before the first time an object of type {{lc|std::ios_base::Init}} is constructed and are available for use in the constructors and destructors of static objects with [[cpp/language/initialization#Non-local_variables|ordered initialization]] (as long as {{tt|<iostream>}} is included before the object is defined). | These objects are guaranteed to be initialized during or before the first time an object of type {{lc|std::ios_base::Init}} is constructed and are available for use in the constructors and destructors of static objects with [[cpp/language/initialization#Non-local_variables|ordered initialization]] (as long as {{tt|<iostream>}} is included before the object is defined). | ||
Unless {{c|sync_with_stdio(false)}} has been issued, it is safe to concurrently access these objects from multiple threads for both formatted and unformatted output. | Unless {{c|sync_with_stdio(false)}} has been issued, it is safe to concurrently access these objects from multiple threads for both formatted and unformatted output. | ||
| + | |||
| + | ===Notes=== | ||
| + | The 'c' in the name refers to "character" ([http://www.stroustrup.com/bs_faq2.html#cout stroustrup.com FAQ]); {{tt|clog}} means "character log" and {{tt|wclog}} means "wide character log" | ||
===Example=== | ===Example=== | ||
Revision as of 07:47, 14 June 2016
| Defined in header <iostream>
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| extern std::ostream clog; |
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| extern std::wostream wclog; |
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The global objects std::clog and std::wclog control output to a stream buffer of implementation-defined type (derived from std::streambuf), associated with the standard C output stream stderr, but, unlike std::cerr/std::wcerr, these streams are not automatically flushed and not automatically tie()'d with cout.
These objects are guaranteed to be initialized during or before the first time an object of type std::ios_base::Init is constructed and are available for use in the constructors and destructors of static objects with ordered initialization (as long as <iostream> is included before the object is defined).
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.
Notes
The 'c' in the name refers to "character" (stroustrup.com FAQ); clog means "character log" and wclog means "wide character log"
Example
#include <iostream> struct Foo { int n; Foo() { std::clog << "static constructor\n"; } ~Foo() { std::clog << "static destructor\n"; } }; Foo f; // static object int main() { std::clog << "main function\n"; }
Output:
static constructor main function static destructor
See also
| initializes standard stream objects (public member class of std::ios_base)
| |
| writes to the standard C error stream stderr, unbuffered (global object) | |
| writes to the standard C output stream stdout (global object) |
