Namespace
Varianti

std::clock

Da cppreference.com.
< cpp‎ | chrono‎ | c

 
 
Utilità libreria
Tipo di supporto (basic types, RTTI, type traits)
Gestione della memoria dinamica
La gestione degli errori
Programma di utilità
Funzioni variadic
Data e ora
Funzione oggetti
initializer_list(C++11)
bitset
hash(C++11)
Gli operatori relazionali
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Relational operators
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rel_ops::operator!=
rel_ops::operator>
rel_ops::operator<=
rel_ops::operator>=
Coppie e tuple
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Pairs and tuples
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pair
tuple(C++11)
piecewise_construct_t(C++11)
piecewise_construct(C++11)
Swap, in avanti e spostare
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Swap, forward and move
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swap
forward(C++11)
move(C++11)
move_if_noexcept(C++11)
declval(C++11)
 
 
C-stile di data e ora utilità
Funzioni
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Functions
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Tempo di manipolazione
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Time manipulation
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difftime
time
clock
Formato conversioni
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Format conversions
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asctime
ctime
strftime
wcsftime
gmtime
localtime
mktime
Costanti
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Constants
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CLOCKS_PER_SEC
Tipi
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Types
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tm
time_t
clock_t
 
Defined in header <ctime>
std::clock_t clock();
Restituisce il tempo approssimativo processore utilizzato dal processo sin dall'inizio di una implementazione definita epoca che riguarda l'esecuzione del programma. Per convertire il valore risultato secondi dividere per CLOCKS_PER_SEC. Poiché l'inizio dell'era std::clock non deve coincidere con l'inizio del programma, solo la differenza tra due valori restituiti da diverse chiamate al std::clock è significativo. Se la CPU è condivisa da altri processi, il tempo std::clock possono avanzare più lento di orologio a muro. Se il processo corrente è multithread e più di un core di esecuzione è disponibile, il tempo std::clock possono avanzare più velocemente di orologio da parete.
Original:
Returns the approximate processor time used by the process since the beginning of an implementation-defined era related to the program's execution. To convert result value to seconds divide it by CLOCKS_PER_SEC. Because the beginning of the std::clock era does not have to coincide with the start of the program, only the difference between two values returned by different calls to std::clock is meaningful. If the CPU is shared by other processes, std::clock time may advance slower than wall clock. If the current process is multithreaded and more than one execution core is available, std::clock time may advance faster than wall clock.
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Indice

[modifica] Parametri

(Nessuno)
Original:
(none)
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[modifica] Valore di ritorno

Tempo processore utilizzato dal programma finora o (clock_t)(-1) se tali informazioni non è più disponibile.
Original:
Processor time used by the program so far or (clock_t)(-1) if that information is unavailable.
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[modifica] Note

In POSIX-compatibili, clock_gettime con id CLOCK_PROCESS_CPUTIME_ID orologio offre una migliore risoluzione.
Original:
On POSIX-compatible systems, clock_gettime with clock id CLOCK_PROCESS_CPUTIME_ID offers better resolution.
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Il valore restituito da clock() può avvolgere attorno in alcune implementazioni. Ad esempio, su una macchina a 32-bit std::clock_t, avvolge dopo 2147 secondi o 36 minuti.
Original:
The value returned by clock() may wrap around on some implementations. For example, on a machine with 32-bit std::clock_t, it wraps after 2147 seconds or 36 minutes.
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clock() non è richiesto di essere thread-safe.
Original:
clock() is not required to be thread-safe.
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[modifica] Esempio

Questo esempio mostra la differenza tra l'orologio () tempo e in tempo reale
Original:
This example demonstrates the difference between clock() time and real time
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#include <iostream>
#include <chrono>
#include <ctime>
#include <thread>
 
// the function f() does some time-consuming work
void f()
{
    volatile double d;
    for(int n=0; n<10000; ++n)
       for(int m=0; m<10000; ++m)
           d += d*n*m;
}
 
int main()
{
    std::clock_t c_start = std::clock();
    auto t_start = std::chrono::high_resolution_clock::now();
    std::thread t1(f); 
    std::thread t2(f); // f() is called on two threads
    t1.join();
    t2.join();
    std::clock_t c_end = std::clock();
    auto t_end = std::chrono::high_resolution_clock::now();
 
    std::cout << "CPU time used: "
              << 1000.0 * (c_end-c_start) / CLOCKS_PER_SEC
              << " ms\n";
    std::cout << "Wall clock time passed: "
              << std::chrono::duration_cast<std::chrono::milliseconds>(t_end - t_start).count()
              << " ms\n";
}

Output:

CPU time used: 1520 ms
Wall clock time passed: 769 ms

[modifica] Vedi anche

converte un oggetto time_t di una rappresentazione testuale
Original:
converts a time_t object to a textual representation
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(funzione) [edit]
restituisce l'ora corrente del sistema nel tempo dal epoca
Original:
returns the current time of the system as time since epoch
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(funzione) [edit]
C documentation for clock