C++ Error using a custom ifstream class with a variable as argument

Question

I am using a custom ifstream class

class plb_ifstream : public Parallel_istream {
public:
plb_ifstream();
explicit plb_ifstream(const char* filename,
                      std::istream::openmode mode = std::ostream::in );
~plb_ifstream();
virtual std::istream& getOriginalStream();

bool is_open();
void open(const char* filename, std::istream::openmode mode = std::ostream::in);
void close();
bool good();
private:
plb_ifstream(plb_ifstream const& rhs);
plb_ifstream& operator=(plb_ifstream const& rhs);
private:
DevNullBuffer devNullBuffer;
std::istream  devNullStream;
std::ifstream *original;

};

This works well with a single file like

plb_ifstream ifile("geometry.dat");

However when I try to use a variable in the argument (in a for-loop) like

for(plint num=1; num<4; num++)
{
    std::ostringstream ostr;
    ostr <<num<<".dat";
    std::string var = ostr.str();

    pcout <<"Reading geometry.."<<endl;
    plb_ifstream ifile(ostr.str());
    ifile >> boolMask;
    pcout<<"done..."<<endl;}

I get the following errors

error: no matching function for call to ‘plb::plb_ifstream::plb_ifstream(std::basic_ostringstream<char>::__string_type)’|
note: candidates are:|
note: plb::plb_ifstream::plb_ifstream(const plb::plb_ifstream&)|
note: no known conversion for argument 1 from ‘std::basic_ostringstream<char>::__string_type {aka std::basic_string<char>}’ to ‘const plb::plb_ifstream&’|
note: plb::plb_ifstream::plb_ifstream(const char*, std::ios_base::openmode)|
note:   no known conversion for argument 1 from ‘std::basic_ostringstream<char>::__string_type {aka std::basic_string<char>}’ to ‘const char*’|
note: plb::plb_ifstream::plb_ifstream()|
note:   candidate expects 0 arguments, 1 provided|

I did find some other solutions but they do not utilize ifstream. If there is a work around using only ifstream them I would appreciate the help

`plb_ifstream ifile(ostr.str().c_str());`? The constructor you have needs a `const char*` not a `std::string` which is what the error says. — Retired Ninja, Mar 17 '15 at 00:31

score 2 · Accepted Answer · answered Mar 17 '15 at 00:31

2

You probably need to replace:

plb_ifstream ifile(ostr.str());

with

plb_ifstream ifile(ostr.str().c_str());

to get C string equivalent

answered Mar 17 '15 at 00:31

Jacob Seleznev

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score 1 · Answer 2 · answered Mar 17 '15 at 00:32

1

You haven't written a plb_ifstream constructor that takes a std::string such as that returned by your std::ostringstream's .str(). Append a further .c_str() or add a constructor.

answered Mar 17 '15 at 00:32

Tony Delroy

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C++ Error using a custom ifstream class with a variable as argument

2 Answers2