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Passing enum constant as function arguments.

Posted on 2004-08-08
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Last Modified: 2010-05-18

Hello Experts,

I am trying to understand the concept of using enum with functions to control program execution. Can someone please explain how can I use/pass enum constant to a function. What would be the function prototype and the syntax of function call.

Here is the code:

#include<stdio.h>

#define SQL1 "select username,user_id from dba_users";

/* Constants defined */
typedef enum oci {RUNSQL1=1} ociprogram;

/* Function prototypes */
int runSql(ociprogram, char *);

int main()
{
       runSql(RUNSQL1,SQL1);   /* Call to runSql - passing RUNSQL and SQL1 */

     return 0;
}


int runSql(ociprogram RUNSQL1, char *ocisql1)
{      
        printf("RunSQL = %d\n");
        printf("SQL statment = %s\n",ocisql1);

        return 0;
}


Thanks!

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Question by:mohammadzahid
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6 Comments
 
LVL 55

Expert Comment

by:Jaime Olivares
ID: 11749667
In your example, you can divide enumeration in 2 parts:

enum oci {RUNSQL=1};   <--- Defines an enumeration called oci with just one value (RUNSQL)

then funtion prototype but be:

int runSql(enum oci, char *)

But, to avoid mention enum keyword every time, it is define with a typedef:

typedef enum oci {RUNSQL1=1} ociprogram;

now you have a new data type: ociprogram, similar to int or char

Thus, the function declaration is now:

int runSql(ociprogram, char *)

That's means that first argument of this function can be ONLY enumerated values, in this case, unique possibility is RUNSQL1, or 1.

Inside runSql there is a bug, first line must be:

       printf("RunSQL = %d\n", RUNSQL1);

It will demonstrate that when you pass RUNSQL1 as first argument, you are really passing value 1.

Hope this help.
Good luck,
Jaime.
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LVL 55

Expert Comment

by:Jaime Olivares
ID: 11749675
I have not noticed another error in your function

int runSql(ociprogram RUNSQL1, char *ocisql1)

It is not convenient to name first argument as RUNSQL1, because will confuse you with enum value,
better you can name it 'value'. So your entire function must be:

int runSql(ociprogram value, char *ocisql1)
{    
       printf("RunSQL = %d\n", value);
       printf("SQL statment = %s\n",ocisql1);

       return 0;
}
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Accepted Solution

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Jaime Olivares earned 1200 total points
ID: 11749687
The fact is that runSql can be invoked only with valid enumerated values, it is a good method to avoid incorrect coding.
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LVL 11

Author Comment

by:mohammadzahid
ID: 11749704
Thanks Jaime for quick response and appreciate your help.

Now I am getting error

e:\vstudionet\Myprojects\testprograms\testprograms\main.c(13) : error C2143: syntax error : missing ')' before ';'

at the function call when calling function  

runSql(RUNSQL1,SQL1);    /* RUNSQL1 is the first const of enum && SQL1 is a string value */

from the main ( ).

Can you please provide syntax of the function call if you don't mind.

Thanks again.


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LVL 55

Expert Comment

by:Jaime Olivares
ID: 11749718
The origin of the problem is in the #define

#define SQL1 "select username,user_id from dba_users";  <---- remove semicolon here
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LVL 11

Author Comment

by:mohammadzahid
ID: 11749739
That solved the problem. Thanks again.

Thread closed.
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