Question

In the stdio, omething like:

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

works fine, but with streams:

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

Gives me some crazy ass compiler error:

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 *)'

I’m assuming this is the c++ equivalent of doing this, but it won’t work. How can I go aboot doing this?

Answer 1

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

What you are telling the compiler to do here is to read a pointer from a file (which doesn’t make a lot of sense). Your fscanf sample does a different thing: It reads an integer from the file. With streams, you can write this as such:

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

By the way, the error message

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

Is trying to tell you that you cannot read a pointer in the way your code suggests, because the >> operator is not defined for the right-hand type int*.