OS_WriteC (changes)

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Programmer's OS Reference SWI Manuals Calls

» OS_WriteCPart 15 – SWI Calls

OS_WriteC

(SWI &00)

Use

The purpose of this call is to send a character to all of the active output streams.

Notes

This SWI sends the byte in R0 to all active output streams (see OS_Byte 3 for specifying a stream). Do not assume that this SWI will never generate an error – it can and occasionally does.

Consider the case where output is redirected to a file on a filing system which has no space. This is the most common example.

A less common, but possible case is where an application displays a string in its Exit handler. Under a TaskWindow, if you close the window before the task has exited, its Exit handler is called. This should tidy up and exit. If it prints strings using non-X versions of the SWIs an error will be generated. This will call the Error handler, which will either display a message or call the Exit handler. In the former case, if X SWIs are used the Exit handler is usually called.

The outcome of this is that a TaskWindow can hog 99% of the processor time as it switches in and out of SVC mode incredibly quickly in an infinite sequence of errors. Avoid this by using X SWIs.

See also

• OS_Byte 3
• OS_Write0
• OS_WriteI
• OS_WriteN
• OS_WriteS
• TaskWindow