CODEWITHSUNDEEP
c++
Sumsar1812
Sumsar1812

Reputation: 618

Can't get ifstream object declared as a member in my class

i am trying to read from a file in multiple places in my class functions. Therefor i thought it would be smart to declare the object in the headerfile(in private) but after i did that it does not work anymore

I did use the search function and found something about copy constructors might be the problem but i don't really know what they do and why i need to change something about them(if that is even the case in my code)

command.h:

class command
{
public:

command();
~command();
void printCommands() const;

private:
std::ifstream file;

}

Command.cpp

command::command(){
file.open("commands.txt");
}
command::~command()
{
file.close();
}
void command::printCommands() const
{
int i = 0;

std::string line;
std::cout <<"Command list:\n\n";

while (getline(file,line))
{
    std::cout << line <<endl<<endl;
}
}

This is just a part of the code but basicly i get an errror at the getline function

i get this error

 error C2665: 'std::getline' : none of the 2 overloads could convert all the argument types
 std::basic_istream<_Elem,_Traits> &std::getline<char,std::char_traits<char>,std::allocator<_Ty>>      (std::basic_istream<_Elem,_Traits> &&,std::basic_string<_Elem,_Traits,_Alloc> &)

edit1:

I did forget, if i do move the 

 std::ifstream file;

into the cpp functions (where i use the getline functions) it works without a problem, but shouldn't it work with the declarition in private?

Upvotes: 1

Views: 361

Answers (2)

bames53
bames53

Reputation: 88155

void command::printCommands() const

That line declares printCommands() to be a const function. I.e., one that does not change the command object. Reading from an input stream is a change, so if the input stream is part of the command then reading from it necessarily changes the command.

I don't know your program so I can't say whether the following is a good idea or not, but it should make the error go away: declare file as a mutable member:

mutable std::ifstream file;

Upvotes: 1

utnapistim
utnapistim

Reputation: 27365

Your command::printCommands() is declared const. Since file is a member, you are trying to pass a const ifstream& as a non-const std::istream& parameter (received by std::getline).

The conversion looses the const qualifier on call (so compilation fails with the error you got).

To fix, remove the const qualifier from command::printCommands().

Upvotes: 2

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