Не можете сделать fstream >> int *?

Question

В stdio, что-то вроде:

int *x = 435345435;
FILE* file = fopen("file", "r");
fscanf(file, "%d", x);

работает нормально, но с потоками:

int *x = 43532;
fstream file("file");
file >> x;

Дает мне сумасшедшую ошибку компилятора задницы:

error C2678: binary '>>' : no operator found which takes a left-hand operand of type 'std::fstream' (or there is no acceptable conversion)
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(1053): could be 'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &&,signed char *)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(1060): or       'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &&,signed char &)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(1067): or       'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &&,unsigned char *)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(1074): or       'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &&,unsigned char &)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(1097): or       'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &,signed char *)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(1104): or       'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &,signed char &)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(1111): or       'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &,unsigned char *)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(1118): or       'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &,unsigned char &)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(1128): or       'std::basic_istream<_Elem,_Traits> &std::operator >><char,std::char_traits<char>,int*>(std::basic_istream<_Elem,_Traits> &&,_Ty &)' [found using argument-dependent lookup]
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>,
1>              _Ty=int *
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(179): or       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(std::basic_istream<_Elem,_Traits> &(__cdecl *)(std::basic_istream<_Elem,_Traits> &))'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(185): or       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(std::basic_ios<_Elem,_Traits> &(__cdecl *)(std::basic_ios<_Elem,_Traits> &))'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(192): or       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(std::ios_base &(__cdecl *)(std::ios_base &))'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(199): or       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(std::_Bool &)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(218): or       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(short &)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(253): or       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(unsigned short &)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(272): or       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(int &)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(298): or       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(unsigned int &)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(316): or       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(long &)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(334): or       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(unsigned long &)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(354): or       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(__int64 &)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(373): or       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(unsigned __int64 &)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(392): or       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(float &)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(411): or       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(double &)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(429): or       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(long double &)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(447): or       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(void *&)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\istream(466): or       'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(std::basic_streambuf<_Elem,_Traits> *)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          while trying to match the argument list '(std::fstream, int *)'

Я предполагаю, что это эквивалентно с ++, но это не сработает.Как я могу пойти и сделать это?

Answer 1

int *x = 43532;
fstream file("file");
file >> x;

Здесь вы говорите компилятору прочитать указатель из файла (что не имеет большого смысла). Ваш fscanf пример делает другое: он читает integer из файла. С потоками вы можете написать это так:

int *x = 43532;
fstream file("file");
file >> *x;

Кстати, сообщение об ошибке

binary '>>' : no operator found which takes a left-hand operand of type 'std::fstream' 
...
while trying to match the argument list '(std::fstream, int *)'

пытается сказать вам, что вы не можете прочитать указатель так, как предлагает ваш код, потому что оператор >> не определен для правого типа int*.

Answer 2

Если вы сделаете указатель, вам нужно использовать *, чтобы получить значение.

x - это указатель, поэтому вам нужно использовать * x.