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11.13 Open Modes

Open and Create calls result in a call to fopen using the mode shown in the following table:

Open and Create Call Modes
Out_File (Direct_IO)"r+""w"
Out_File (all other cases)"w""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.