std::basic_filebuf<CharT, Traits>* open( const char* s, std::ios_base::openmode mode ) | (1) | |
std::basic_filebuf<CharT, Traits>* open( const std::string& str, std::ios_base::openmode mode ) | (2) | (since C++11) |
Opens the file with the given name - either s or str.c_str().
The file is opened as if by calling std::fopen(s, modestring), where modestring is determined as follows:
| modestring | openmode & ~ate | Action if file already exists | Action if file does not exist |
|---|---|---|---|
| "r" | in | Read from start | Failure to open |
| "w" | out, out|trunc | Destroy contents | Create new |
| "a" | app, out|app | Append to file | Create new |
| "r+" | out|in | Read from start | Error |
| "w+" | out|in|trunc | Destroy contents | Create new |
| "a+" | out|in|app, in|app | Write to end | Create new |
| "rb" | binary|in | Read from start | Failure to open |
| "wb" | binary|out, binary|out|trunc | Destroy contents | Create new |
| "ab" | binary|app, binary|out|app | Write to end | Create new |
| "r+b" | binary|out|in | Read from start | Error |
| "w+b" | binary|out|in|trunc | Destroy contents | Create new |
| "a+b" | binary|out|in|app, binary|in|app | Write to end | Create new |
If openmode is not one of the modes listed, the open() fails.
If the open operation succeeds and openmode & std::ios_base::ate != 0 (the ate bit is set), repositions the file position to the end of file, as if by calling std::fseek(file, 0, SEEK_END). If the repositioning fails, calls close() and returns a null pointer to indicate failure.
If the associated file was already open, returns a null pointer right away.
Parameters
| s, str | - | the file name to open |
| openmode | - | the file opening mode, a binary OR of the std::ios_base modes |
Return value
this on success, a null pointer on failure.
Notes
open() is typically called through the constructor or the open() member function of std::basic_fstream.
Example
See also
| checks if the associated file is open (public member function) | |
| flushes the put area buffer and closes the associated file (public member function) |
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