How do I set a structure pointer variable to default value NULL in a function parameter?

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struct queue{
    int value;
    struct queue *tlink;
    struct queue *blink;
};

typedef struct queue* Q;

void enqueue(Q top, int val, Q bottom=NULL);

error:

expected ‘;’, ‘,’ or ‘)’ before ‘=’ token
void enqueue(Q top, int val, Q bottom=NULL);

What I have tried:

I am trying to initialise a structure pointer variable to default value NULL in function parameter. (Default parameter)

Posted 25-Dec-17 20:00pm

R Hegde

Updated 25-Dec-17 20:57pm

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Peter_in_2780 26-Dec-17 2:54am

The C language (unlike many of its derivatives) doesn't do default parameters. You'll need to find another way to express what you want to achieve.

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OriginalGriff · Accepted Answer · 2017-12-25T20:56:00

C doesn't have any concept of default parameters, so you pretty much can't do that.

(Which is a lie-to-children, becuase you can, but it's horribly complicated and messy: C default arguments - Stack Overflow[^] - see BK's solution, which TBH is worse than the original problem from a maintenance POV).