Question

I am using two compilers g++ and Dev – C++. when I compile my program on Dev-C++ it compiles perfectly. but when i try to compile it on g++ it gives me two errors:

In file included from a2test.cpp:27:
----.h:25: error: 'ostream' has not been declared
----.h:26: error: 'istream' has not been declared

Can anyone tell me what can I do to solve this problem.

Thanks

Answer 1

Make sure you include fstream. Also, put “std::” before ostream or put “using namespace std” somewhere.

It would help if you posted the code, as right now I’m just guessing based on common mistakes.

I would guess you forgot to include fstream because different compilers may use different header files and it may be the case that g++ has a header file with

// iostream
#include <fstream>

While Dev-C++ may have

// iostream
// no include for fstream in this file

So you’re accidentally importing the correct header file rather than doing it explicitly.

For header files, I just use this site when I forget which one.

ostream – C++ Reference

It seems you need to include ostream to get ostream. Probably the same thing for istream.