basic_filebuf::open

basic_filebuf::open

basic_filebuf *open(const char *s, ios_base::openmode mode);

The member function endeavors to open the file with file name s, by calling fopen``(s, strmode). Here strmode is determined from mode & ~(ate& |binary):

• ios_base::in becomes "r" (open existing file for reading).
• ios_base::out or
• ios_base::``out`` | ios_base::trunc becomes "w" (truncate existing file or create for writing).
• ios_base::``out`` | app becomes "a" (open existing file for appending all writes).
• ios_base::``in`` | ios_base::``out becomes "r+" (open existing file for reading and writing).
• ios_base::``in`` | ios_base::``out`` | ios_base::``trunc becomes "w+" (truncate existing file or create for reading and writing).
• ios_base::``in`` | ios_base::``out`` | ios_base::``app becomes "a+" (open existing file for reading and for appending all writes).

If mode & ios_base::``binary is nonzero, the function appends b to strmode to open a binary stream instead of a text stream. It then stores the value returned by fopen in the file pointerfp. If mode & ios_base::``ate is nonzero and the file pointer is not a null pointer, the function calls fseek``(fp, 0, ``SEEK_END``) to position the stream at end-of-file. If that positioning operation fails, the function calls close(fp) and stores a null pointer in the file pointer.

If the file pointer is not a null pointer, the function determines the file conversion facetuse_facet< codecvt<E, char, T::state_type> >(getloc()), for use by underflow and overflow.

If the file pointer is a null pointer, the function returns a null pointer. Otherwise, it returns this.