scanf doesn't like order of input

This is a discussion on scanf doesn't like order of input within the C Programming forums, part of the General Programming Boards category; Yes, I know I shouldn't be using scanf. I'd still like to know why this doesn't work though. With scanf ...

  1. #1
    Registered User
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    May 2006
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    scanf doesn't like order of input

    Yes, I know I shouldn't be using scanf. I'd still like to know why this doesn't work though.

    With scanf reading into the float variable first, it shows up as 0.0000... but the double variable shows up fine.

    With scanf reading the double variable first, both numbers print out exactly as they should. Why is this?

    Code:
    #include <stdio.h>
    
    union floatingPoint {
    	float f;
    	double d;
    	long double x;
    } test[ 3 ];
    
    int main()
    {
    	int i;
    
    	scanf( "%f%lf", &(test[ 0 ].f), &(test[ 0 ].d) );
    	printf( "%f %lf\n", test[ 0 ].f, test[ 0 ].d );
    
    	return 0;
    }

    Code:
    eugene@eugene-laptop:~/cfiles$ ./a.out
    1 1
    0.000000 1.000000

  2. #2
    and the hat of wrongness Salem's Avatar
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    Perhaps it has something to do with using a union rather than a struct.
    Largest one, or last one wins (basically).

    Double first only "works" with small integers, because the LSW of the double is all zeros anyway.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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  3. #3
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    ahh, thanks.

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