Question

Does open function have some sort of restriction as to what kind of string value is passed in?

ifstream file;
string filename = "output.txt";
file.open(filename);

I tried to pass a string value with a string variable, but when it tries to compile, the result is…

agent.cpp:2:20: error: ofstream: No such file or directory
agent.cpp: In function ‘std::string readingline(std::string)’:
agent.cpp:11: error: aggregate ‘std::ifstream file’ has incomplete type and cannot be     defined
agent.cpp: In function ‘int main()’:
agent.cpp:44: error: aggregate ‘std::ofstream writefile’ has incomplete type and cannot be defined

On the other hand, when I just pass a string value in quotes like “filename.txt” , it compile fine and runs fine.

ifstream file;
file.open("output.txt");

Why is this the case?

Is there a way to solve this problem?

Answer 1

Sadly, this is how the constructor and open of std::(i|o)fstream are defined by the standard. Use file.open(filename.c_str()).

Some standard libraries provide an extension that allows std::string as a parameter, e.g. Visual Studio.