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scanf conflicting characters remain in the input stream

Georg Bunter

hello, there's a little problem with the scanf-function. My program

...
 scanf("%u",&A);
...
expects a unsigned integer. But when someone hits a unwanted character, scanf terminates. Any conflicting character remain in the input stream. How to clear the scanf-input-stream? Is there a known workaround for ARM7 ADuC7026)? In C51 you just 
CLR ?C?charloaded
RET
But how on ARM7? Thanks for advice :-)

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  • 0 in reply to Patrick Noonan

    the Keil C51 does have an input buffer that needs to be cleared.

    That's an over-interpretaion of that support note you found. Yes, it does have a buffer, which you can clear if you want to. But by no means does that imply it needs to be cleared. In a nutshell: if you feel a need to clear stdin, you've quite invariably done something wrong before, i.e. you're now trying to fix symptoms instead of treating the disease.

    Basically, scanf() directly into any other format but strings is hardly ever an appropriate means of reading input from a non-deterministic source, e.g. a human operator. I.e. if you don't know for sure that the input will exactly match your scanf() format, every time, then scanf() is the wrong function to use. As I already indicated, error-prone input pretty much has to be read as a string, which you then sscanf().

Reply
  • 0 in reply to Patrick Noonan

    the Keil C51 does have an input buffer that needs to be cleared.

    That's an over-interpretaion of that support note you found. Yes, it does have a buffer, which you can clear if you want to. But by no means does that imply it needs to be cleared. In a nutshell: if you feel a need to clear stdin, you've quite invariably done something wrong before, i.e. you're now trying to fix symptoms instead of treating the disease.

    Basically, scanf() directly into any other format but strings is hardly ever an appropriate means of reading input from a non-deterministic source, e.g. a human operator. I.e. if you don't know for sure that the input will exactly match your scanf() format, every time, then scanf() is the wrong function to use. As I already indicated, error-prone input pretty much has to be read as a string, which you then sscanf().

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  • 0 in reply to HansBernhard Broeker

    Hans,

    That's an over-interpretaion of that support note you found.
Yes, it does have a buffer, which you can clear if you want to.
But by no means does that imply it needs to be cleared

    I think maybe you misinterpreted my post. You need to clear it only (on the C51 scanf) if unwanted characters appear was my intended meaning. I thought that was clear from the context of the thread but maybe not. I certainly was not suggesting that it should be done as a matter-of-course. :)