C++ Fstream Library - Open Function

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Description

Opens the file identified by argument filename, associating it with the stream object, so that input/output operations are performed on its content. Argument mode specifies the opening mode.

Declaration

Following is the declaration for fstream::open.

C++98

 void open (const char* filename,ios_base::openmode mode = ios_base::in | ios_base::out); 

C++11

 void open (const char* filename,ios_base::openmode mode = ios_base::in | ios_base::out); void open (const string& filename,ios_base::openmode mode = ios_base::in | ios_base::out); 

Parameters

• filename − String with the name of the file to open,Specifics about its format and validity depend on the library implementation and running environment.

• mode − Flags describing the requested input/output mode for the file.

Return Value

• none

• If the function fails to open a file, the failbit state flag is set for the stream (which may throw ios_base::failure if that state flag was registered using member exceptions).

Exceptions

• Basic guarantee − if an exception is thrown, the stream is in a valid state.

• It throws an exception of member type failure if the function fails (setting the failbit state flag) and member exceptions was set to throw for that state.

Data races

• Modifies the fstream object.

• Concurrent access to the same stream object introduce data races.

Example

In below example explains about fstream open function.

 #include <fstream> int main () { std::fstream fs; fs.open ("test.txt", std::fstream::in | std::fstream::out | std::fstream::app); fs << " more lorem ipsum"; fs.close(); return 0; }