Perché iostream include time.h?

Considerate questo codice:Perché iostream include time.h?

#include <iostream> 

template<class C> 
struct time { }; 

int main() { }

Produce (GCC 4.5):

error: ‘template<class C> struct time’ redeclared as different kind of symbol 
/usr/include/time.h:186:15: error: previous declaration of ‘time_t time(time_t*)’

Perché iostream includono time_t time(time_t*)?
Perché lo iostream include time_t time(time_t*) nello spazio dei nomi std?
(senza risposta) Perché, se rimuovo template<class C>, non viene visualizzato questo errore?

fonte

2011-11-04 Ruggero Turra

Se si esegue g++ -H -Wall -c testim.cc (dove testim.cc è il vostro esempio) vedrai che

.... /usr/include/c++/4.6/bits/ios_base.h 
..... /usr/include/c++/4.6/ext/atomicity.h 
...... /usr/include/c++/4.6/x86_64-linux-gnu/./bits/gthr.h 
....... /usr/include/c++/4.6/x86_64-linux-gnu/./bits/gthr-default.h 
........ /usr/include/pthread.h 
......... /usr/include/sched.h 
.......... /usr/lib/gcc/x86_64-linux-gnu/4.6/include/stddef.h 
.......... /usr/include/time.h

Così <time.h> è incluso per supporto pthread.

questo è con GCC 4.6 su Debian/Sid/AMD64

fonte

2011-11-04 23:10:02

Provalo su 4.6.2. Il log delle modifiche dice che la dipendenza da "" è stata ridotta. –

Sulla mia macchina g ++ è 'gcc versione 4.6.2 (Debian 4.6.2-3)' –

sembra essere per il supporto locale sulla mia macchina:

$ cat whytime.cc 
#define _TIME_H_ 
#include <iostream> 

int main() { 
    std::cout << "hello, world" << std::endl; 
    return 0; 
} 

$ g++ -Wall -Werror -Wextra -ansi -o whytime whytime.cc && ./whytime 
In file included from /usr/include/c++/4.2.1/cwchar:52, 
       from /usr/include/c++/4.2.1/bits/postypes.h:46, 
       from /usr/include/c++/4.2.1/iosfwd:49, 
       from /usr/include/c++/4.2.1/ios:43, 
       from /usr/include/c++/4.2.1/ostream:45, 
       from /usr/include/c++/4.2.1/iostream:45, 
       from whytime.cc:2: 
/usr/include/c++/4.2.1/ctime:66: error: ‘::clock_t’ has not been declared 
/usr/include/c++/4.2.1/ctime:68: error: ‘::tm’ has not been declared 
/usr/include/c++/4.2.1/ctime:70: error: ‘::clock’ has not been declared 
/usr/include/c++/4.2.1/ctime:71: error: ‘::difftime’ has not been declared 
/usr/include/c++/4.2.1/ctime:72: error: ‘::mktime’ has not been declared 
/usr/include/c++/4.2.1/ctime:73: error: ‘::time’ has not been declared 
/usr/include/c++/4.2.1/ctime:74: error: ‘::asctime’ has not been declared 
/usr/include/c++/4.2.1/ctime:75: error: ‘::ctime’ has not been declared 
/usr/include/c++/4.2.1/ctime:76: error: ‘::gmtime’ has not been declared 
/usr/include/c++/4.2.1/ctime:77: error: ‘::localtime’ has not been declared 
/usr/include/c++/4.2.1/ctime:78: error: ‘::strftime’ has not been declared 
In file included from /usr/include/c++/4.2.1/locale:46, 
       from /usr/include/c++/4.2.1/bits/ostream.tcc:46, 
       from /usr/include/c++/4.2.1/ostream:572, 
       from /usr/include/c++/4.2.1/iostream:45, 
       from whytime.cc:2: 
/usr/include/c++/4.2.1/bits/locale_facets.tcc: In member function ‘_InIter std::time_get<_CharT, _InIter>::_M_extract_via_format(_InIter, _InIter, std::ios_base&, std::_Ios_Iostate&, tm*, const _CharT*) const’: 
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1839: error: invalid use of incomplete type ‘struct tm’ 
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’ 
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1846: error: invalid use of incomplete type ‘struct tm’ 
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’ 
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1854: error: invalid use of incomplete type ‘struct tm’ 
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’ 
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1861: error: invalid use of incomplete type ‘struct tm’ 
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’ 
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1873: error: invalid use of incomplete type ‘struct tm’ 
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’ 
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1880: error: invalid use of incomplete type ‘struct tm’ 
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’ 
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1883: error: invalid use of incomplete type ‘struct tm’ 
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’ 
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1895: error: invalid use of incomplete type ‘struct tm’ 
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’ 
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1900: error: invalid use of incomplete type ‘struct tm’ 
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’ 
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1908: error: invalid use of incomplete type ‘struct tm’ 
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’ 
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1912: error: invalid use of incomplete type ‘struct tm’ 
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’ 
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1932: error: invalid use of incomplete type ‘struct tm’ 
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’ 
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1968: error: invalid use of incomplete type ‘struct tm’ 
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’ 
/usr/include/c++/4.2.1/bits/locale_facets.tcc:1976: error: invalid use of incomplete type ‘struct tm’ 
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’ 
/usr/include/c++/4.2.1/bits/locale_facets.tcc: In member function ‘virtual _InIter std::time_get<_CharT, _InIter>::do_get_weekday(_InIter, _InIter, std::ios_base&, std::_Ios_Iostate&, tm*) const’: 
/usr/include/c++/4.2.1/bits/locale_facets.tcc:2210: error: invalid use of incomplete type ‘struct tm’ 
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’ 
/usr/include/c++/4.2.1/bits/locale_facets.tcc: In member function ‘virtual _InIter std::time_get<_CharT, _InIter>::do_get_monthname(_InIter, _InIter, std::ios_base&, std::_Ios_Iostate&, tm*) const’: 
/usr/include/c++/4.2.1/bits/locale_facets.tcc:2259: error: invalid use of incomplete type ‘struct tm’ 
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’ 
/usr/include/c++/4.2.1/bits/locale_facets.tcc: In member function ‘virtual _InIter std::time_get<_CharT, _InIter>::do_get_year(_InIter, _InIter, std::ios_base&, std::_Ios_Iostate&, tm*) const’: 
/usr/include/c++/4.2.1/bits/locale_facets.tcc:2288: error: invalid use of incomplete type ‘struct tm’ 
/usr/include/wchar.h:152: error: forward declaration of ‘struct tm’

fonte

2011-11-04 23:05:29 phs

buon trucco, ma non ho il tuo errore –

Definendo la guardia di intestazione di 'time.h', forziamo la sua inclusione a non fare nulla. Presumibilmente, qualunque cosa includa lo userà anche poco dopo, e gli errori di compilazione che ne conseguiranno colpiranno il compratore in flagrante. Per quanto mi riguarda, sembra che/usr/include/C++/4.2.1/locale' sia introdotto da 'ostream'. Si dovrebbe ricordare che questo mostra solo un compratore, ci possono essere altri. – phs

A quanto pare del GCC iostream ha bisogno di qualcosa in time per qualcosa.

time_t è una cosa C lingua, che non ha spazi dei nomi, e quindi per la comparabilità a ritroso-ish, è in entrambi i std spazio dei nomi, e non nel std namespace.

Per quanto riguarda il motivo per cui non ci sono errori, non sono sicuro al 100%. So che lo C potrebbe avere funzioni e strutture con lo stesso nome e gli struct sono stati qualificati con il nome struct in modo che il compilatore potesse distinguerli. I compilatori C++ pensano che sia una funzione, a meno che non sia preceduta dalla parola chiave struct. http://ideone.com/XZB2M v http://ideone.com/kWMKE. Immagino che permetta anche quella di comparabilità al contrario?

fonte

2011-11-04 23:11:02

phs dice che include 'ctime' per il supporto locale, che ha un certo senso. –

ok, ma per quanto riguarda 'template'? –

Non ne ho assolutamente idea. Scusate :( –

Perché iostream include time.h?

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