Unions?

This is a discussion on Unions? within the C Programming forums, part of the General Programming Boards category; What i Gotta DO: Your solution must include a function called displayUnion() which will take a integer_union variable as a ...

  1. #1
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    Unions?

    What i Gotta DO:

    Your solution must include a function called displayUnion() which will take a integer_union variable as a parameter. The function will have simply 4 printf statements, and nothing else! This function will need to be invoked 4 times from the main() program.

    Create a union called "integer_union" with members char c, short s, int i and long l. Each union variable should be printed as a char, a short, an int and a long.

    char: w
    short: 1234
    int: 1234567
    long: 1234567890

    What i got:
    Code:
    #include<stdio.h>
    
    union integer_union{
    	char  c;
    	short s;
    	int   i;
    	long  l;
    };
    int main()
    {
    	union integer_union value;
    	
    	
    	printf( "Please enter a char: " );
    	scanf( "%c", &value.c, "%hd", value.s, "%d", &value.i, "%ld", &value.l );
    	printf( "char  c = %c\nshort s = %hd\nint   i = %d\nlong  l = %ld", value.c, value.s, value.i, value.l );
    
    	printf( "\n\nPlease enter a short: ");
    	scanf( "%hd", &value.c, "%hd", &value.s, "%d", &value.i, "%ld", &value.l );
    	printf( "char  c = %c\nshort s = %hd\nint   i = %d\nlong  l = %ld", value.c, value.s, value.i, value.l );
    	 
    	printf( "\n\nPlease enter a int: ");
    	scanf( "%d", &value.c, "%hd", &value.s, "%d", &value.i, "%ld", &value.l );
    	printf( "char  c = %c\nshort s = %hd\nint   i = %d\nlong  l = %ld", value.c, value.s, value.i, value.l );
    	
    	printf( "\n\nPlease enter a long: ");
    	scanf( "%ld", &value.c, "%hd", &value.s, "%d", &value.i, "%ld", &value.l );
    	printf( "char  c = %c\nshort s = %hd\nint   i = %d\nlong  l = %ld\n\n", value.c, value.s, value.i, value.l );
    	
    	return 0;
    
    }

    It works but im not sure if this is the right way , not sure bout the function called displayUnion() how to implement it er what?

  2. #2
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    If i do something like this it messes up
    Code:
    #include <stdio.h>
    
    
    void display_union();
    
    union integer_union {
    	char c;
    	short s;
    	int i;
    	long l;
    };
    
    int main()
    {
    	char c;
    	short s;
    	int i;
    	long l;
    
    	union integer_union integer_union;
    
    	printf( "please enter a char: " );
    	scanf( "%c", &c );
    
    		integer_union.c = c;
    		display_union();
    
    	printf( "Please enter a short: " );
    	scanf( "%hd", &s );
    
    		integer_union.s = s;
    		display_union();
    
    	printf( "Please enter an int: " );
    	scanf( "%d", &i );
    
    		integer_union.i = i;
    		display_union();
    
    	printf( "Please enter a long: " );
    	scanf( "%ld", &l );
    
    		integer_union.l = l;
    		display_union();
    
    	return 0;
    
    }
    
    void display_union( char c, short s, int i, long l )
    {
    	printf( "char c = %c\n", c );
    	printf( "short s = %hd\n", s );
    	printf( "int i = %i\n", i );
    	printf( "long l = %ld\n\n", l );
    }

  3. #3
    ATH0 quzah's Avatar
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    Do you know how to pass a structure to a function? You pass unions in the same manner. What it sounds like from your description is that you want a function that will be called like so:
    Code:
    union foo
    {
        ...stuff...
    };
    
    union foo bar; /* an instance of the type union foo */
    
    ...do something with bar...
    
    myfunction( bar );
    I'll leave that for you to think on. It's an easy implementation. Post back if you're still stuck with what you've tried.


    Quzah.
    Hope is the first step on the road to disappointment.

  4. #4
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    well still dont understand ... no diff in codes.. damn it .. brain hurts

  5. #5
    and the hat of wrongness Salem's Avatar
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    > If i do something like this it messes up
    Here's your prototype
    void display_union();

    Here's your definition
    void display_union( char c, short s, int i, long l )

    Spot the difference.

    If your compiler doesn't complain, add more warning levels or get a better compiler.
    If your compiler does complain, start paying attention to what it says.

    Here's my warnings
    Code:
    $ gcc -W -Wall -ansi -pedantic foo.c
    foo.c:51: error: conflicting types for 'display_union'
    foo.c:51: note: an argument type that has a default promotion can't match an empty parameter name list declaration
    foo.c:4: error: previous declaration of 'display_union' was here
    foo.c:51: error: conflicting types for 'display_union'
    foo.c:51: note: an argument type that has a default promotion can't match an empty parameter name list declaration
    foo.c:4: error: previous declaration of 'display_union' was here
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  6. #6
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    Hows this... it works
    Code:
    #include <stdio.h>
    
    
    void display_union(char c, short s, int i, long l);
    
    union integer_union {
    	char c;
    	short s;
    	int i;
    	long l;
    };
    
    int main()
    {
    	union integer_union value;
    
    	printf( "Please enter a char: " );
    	scanf( "%c", &value.c, "%hd", value.s, "%d", &value.i, "%ld", &value.l );
    	display_union( value.c,value.s,value.i,value.l);
    
    	printf( "Please enter a short: ");
    	scanf( "%hd", &value.c, "%hd", &value.s, "%d", &value.i, "%ld", &value.l );
    	display_union(value.c,value.s,value.i,value.l);
    
    	printf( "Please enter a int: ");
    	scanf( "%d", &value.c, "%hd", &value.s, "%d", &value.i, "%ld", &value.l );
    	display_union(value.c,value.s,value.i,value.l);
    
    	printf( "Please enter a long: ");
    	scanf( "%ld", &value.c, "%hd", &value.s, "%d", &value.i, "%ld", &value.l );
    	display_union(value.c,value.s,value.i,value.l);
    
    	return 0;
    
    }
    
    void display_union( char c, short s, int i, long l )
    {
    	printf( "char  c = %c\n", c );
    	printf( "short s = %hd\n", s );
    	printf( "int   i = %i\n", i );
    	printf( "long  l = %ld\n\n", l );
    }

  7. #7
    Geek. Cobras2's Avatar
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    Quote Originally Posted by Sure
    Hows this... it works
    Code:
    void display_union(char c, short s, int i, long l);
    I think you're supposed to be passing the *union* to the function, not each of the contents of the union. so like Quzah said, instead of the way you have it above, do this:
    Code:
    void display_union(integer_union u);
    then figure out how to pass the union into that function, instead of passing the members of the union (quzah already said how to do it)
    Last edited by Cobras2; 06-29-2005 at 01:48 AM.
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  8. #8
    Zed
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    scanf( "%c", &value.c, "%hd", value.s, "%d", &value.i, "%ld", &value.l );
    When you are using union, you are permitted to use on variable at a time only.
    that is , use either value.c or value.s or value.i or value.l

    If you want to use all of these, use strcuture.

  9. #9
    ATH0 quzah's Avatar
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    Technically, they are only using one at a time, since everything is done sequentially. Or rather, they would be using them one at a time if that statement wasn't so horribly horribly wrong.


    Quzah.
    Hope is the first step on the road to disappointment.

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