Difference between revisions of "cpp/io/clog"
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{{cpp/title|clog|wclog}} | {{cpp/title|clog|wclog}} | ||
− | {{cpp/io/basic_ostream/ | + | {{cpp/io/basic_ostream/navbar}} |
− | {{ | + | {{dcl begin}} |
− | {{ | + | {{dcl header|iostream}} |
− | {{ | + | {{dcl|num=1|1= |
extern std::ostream clog; | extern std::ostream clog; | ||
}} | }} | ||
− | {{ | + | {{dcl|num=2|1= |
extern std::wostream wclog; | extern std::wostream wclog; | ||
}} | }} | ||
− | {{ | + | {{dcl end}} |
− | 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 cout is not automatically tie()'d with these streams. |
− | These objects are guaranteed to be | + | 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 {{header|iostream}} is included before the object is defined). |
− | Unless {{ | + | Unless {{c|std::ios_base::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" ([https://www.stroustrup.com/bs_faq2.html#cout stroustrup.com FAQ]); {{tt|clog}} means "character log" and {{tt|wclog}} means "wide character log". | ||
===Example=== | ===Example=== | ||
− | {{example | + | {{example |
− | + | |code= | |
#include <iostream> | #include <iostream> | ||
− | struct Foo { | + | |
+ | struct Foo | ||
+ | { | ||
int n; | int n; | ||
− | Foo() { | + | Foo() |
− | + | { | |
+ | std::clog << "static constructor\n"; | ||
} | } | ||
− | ~Foo() { | + | ~Foo() |
− | + | { | |
+ | std::clog << "static destructor\n"; | ||
} | } | ||
}; | }; | ||
+ | |||
Foo f; // static object | Foo f; // static object | ||
+ | |||
int main() | int main() | ||
{ | { | ||
std::clog << "main function\n"; | std::clog << "main function\n"; | ||
} | } | ||
− | + | |output= | |
static constructor | static constructor | ||
main function | main function | ||
Line 42: | Line 51: | ||
===See also=== | ===See also=== | ||
− | {{ | + | {{dsc begin}} |
− | {{ | + | {{dsc inc|cpp/io/ios_base/dsc Init}} |
− | {{ | + | {{dsc inc|cpp/io/dsc cerr}} |
+ | {{dsc inc|cpp/io/dsc cout}} | ||
+ | {{dsc inc|cpp/io/c/dsc std streams}} | ||
+ | {{dsc end}} | ||
+ | |||
+ | {{langlinks|de|es|fr|it|ja|pt|ru|zh}} |
Latest revision as of 11:37, 11 September 2023
Defined in header <iostream>
|
||
extern std::ostream clog; |
(1) | |
extern std::wostream wclog; |
(2) | |
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 cout is not automatically tie()'d with these streams.
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 std::ios_base::sync_with_stdio(false) has been issued, it is safe to concurrently access these objects from multiple threads for both formatted and unformatted output.
[edit] Notes
The 'c' in the name refers to "character" (stroustrup.com FAQ); clog
means "character log" and wclog
means "wide character log".
[edit] 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
[edit] 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) | |
expression of type FILE* associated with the input streamexpression of type FILE* associated with the output streamexpression of type FILE* associated with the error output stream (macro constant) |