翻译强力驱动i was testing with flags in file stream objects the other day
And i did this.
fstream binf("h.txt", ios::app); binf << "hey";With fstream since i didnt use ios::out, the output operation shouldnt have worked , but it does work
I noticed that the the output operation works with ios::app only but if i use any other flag without ios::out it doesnt work
Can anyone tell me why I was able to output to the file while using only ios::app without ios::out
Using app implies out.
The standard specifies that app and out|app have the same result, equivalent to C fopen in mode "a".
Well, appending implies writing, that's about the longest explanation I can come up with.
This answer is more compiler specific,but they are amazing to be noticed:-
VS 2010
fstream:- ios_base::out flag is already set
explicit basic_ofstream(const char *_Filename, ios_base::openmode _Mode = ios_base::out, int _Prot = (int)ios_base::_Openprot) : _Mybase(&_Filebuffer) { if (_Filebuffer.open(_Filename, _Mode | ios_base::out, _Prot) == 0) _Myios::setstate(ios_base::failbit); }GCC 4.5
fstream:- Again ios_base::out flag is already set
explicit basic_ofstream(const char* __s, ios_base::openmode __mode = ios_base::out|ios_base::trunc) : __ostream_type(), _M_filebuf() { this->init(&_M_filebuf); this->open(__s, __mode); } void open(const char* __s, ios_base::openmode __mode = ios_base::out | ios_base::trunc) { if (!_M_filebuf.open(__s, __mode | ios_base::out)) this->setstate(ios_base::failbit); else this->clear(); }And even more interesting thing is, only in ios_base::in the last bit is a 1.Which signifies ios_base::in is able to retain its identity even raised with flag ios_base::out.