How to operator overload fstream in a new class? [duplicate]

Question

I want to wrap a new class to generate a file and make some auto resource recycle and some additional operate with the new file. So I make a new class like

class TmpFile { private: std::string tmp_file_name; std::ofstream tmp_file; public: TmpFile(const std::string &name) :tmp_file_name(name), tmp_file(tmp_file_name, ios::out | ios::trunc) {} ~TmpFile() { tmp_file.close(); //some operate afterwards using tmp_file ... } };

But is there a way to operator overload "<<" to write into file inside "class TmpFile" like

TmpFile f; f << "asd";

You do it same way(s) as with all other binary operators. See What are the basic rules and idioms for operator overloading? for all the gritty details. — molbdnilo
– molbdnilo, Commented Oct 31, 2023 at 9:54

Austin Yang · Accepted Answer · 2023-10-31 10:21:05Z

If you want to accept only one object with "<<" operator, you can directly override it:

class TmpFile { private: std::string tmp_file_name; std::ofstream tmp_file; public: TmpFile(const std::string &name) :tmp_file_name(name), tmp_file(tmp_file_name, ios::out | ios::trunc) {} ~TmpFile() { tmp_file.close(); //some operate afterwards using tmp_file ... } // here define your operator void operator << (const std::string& str) { // do something } };

If you want to accept multiple object with a single operator << , you can check how Eigen library implement like this, for example:

f << "asdf", "efsjkfl"

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