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Open and Create calls result in a call to fopen using the mode shown in the following table:
| Open and Create Call Modes |
| |
|---|---|---|
|
`OPEN' |
`CREATE' | |
| Append_File |
"r+" |
"w+" |
| In_File |
"r" |
"w+" |
| Out_File (Direct_IO) |
"r+" |
"w" |
| Out_File (all other cases) |
"w" |
"w" |
| Inout_File |
"r+" |
"w+"
|
If text file translation is required, then either b or t
is added to the mode, depending on the setting of Text. Text file
translation refers to the mapping of CR/LF sequences in an external file
to LF characters internally. This mapping only occurs in DOS and
DOS-like systems, and is not relevant to other systems.
A special case occurs with Stream_IO. As shown in the above table, the
file is initially opened in r or w mode for the
In_File and Out_File cases. If a Set_Mode operation
subsequently requires switching from reading to writing or vice-versa,
then the file is reopened in r+ mode to permit the required operation.